Troubleshooting for App Inventor 2

More Troubleshooting Help Topics

If you are having trouble with the emulator or USB, the first thing to do is to visit the Connection Test Page to verify that aiStarter is running and that you have installed the latest version of the setup software. Even if the test passes, it is still a good idea to begin your troubleshooting by reinstalling the setup software, making sure to follow all the instructions, including the steps of rebooting and uninstalling. See How to update the App Inventor setup software. Also, in addition to the troubleshooting suggestions shown here, you can find help with problems connecting to the emulator, phone or tablet, and help with aiStarter on the page for General connection help. You can also visit the App Inventor Forum to connect with other App Inventor users.

Auto Update Issues

Auto Update Doesn't Appear to Work for me.

I'm using the emulator and it says that my Companion is out of date.

If you are using the emulator and you see this message, it most likely means that you are using old setup tools. Go to our test page to verify your setup, and install the latest version if necessary. Be sure to follow the instructions about uninstalling and reinstalling, including the rebooting steps.

The Companion within the Emulator display an errors message when I attempt the update.

Make sure your firewall is permitting connections to That is where the new version of the Companion is being downloaded from. The Companion can't update if that address is being blocked.

After the Update, I start the Companion in the Emulator and is fails, saying there isn't a WiFi Connection.

Use the Connect->Reset Connections menu in App Inventor to reset the Emulator and then connect again.

Using the Emulator

I'm trying to use the emulator, and it's not working.

See the Emulator Connection Help Guide

When connecting to the emulator, App Inventor says: "Network Error Communicating with Companion. Try resetting the Companion and reconnecting."

This message means that App Inventor believes that it's connected (to the emulator), but it is getting no response from the AI Companion software that should be running in the emulator. The most common cause here is that App Inventor setup software needs to be reinstalled. To install, you need to first reboot the system, then run the uninstaller for the old version on the tools, then download and install the new tools. If this does not help, see the steps under Emulator Connection Help Guide.

My app runs on the emulator, but images do not appear.

Some people have observed a problem where the app runs on the emulator, but images do not appear. To fix this, reload the App Inventor page in your browser. (Use shift-reload to also reload the cache.) Then try connecting to the emulator again.

Using the USB cable

My device is plugged in, but when I select to connect with USB, I get the message "App Inventor does not see the device".

Unplug the phone, wait 5 seconds and plug it in again. App Inventor should resume connecting automatically.

App Inventor Setup Software

How do I update the App Inventor Setup software?

See the instructions at How to update the App Inventor setup software.

The aiStarter program

App Inventor is telling me to restart the aiStarter program. What is that?

The aiStarter program is installed on your computer when you install the App Inventor Setup software. It provides communication between App Inventor running in the browser, and other parts of App Inventor. Whenever you want to use the emulator or the USB cable, you need to make sure that aiStarter is running. If it is not running, you'll get an error message saying that aiStarter does not appear to be running. On Windows, there should be a button on your desktop that starts aiStarter. On the Mac, aiStarter should start automatically, so Mac users should not have to worry about this. In case aiStarter somehow does need to be started manually on the Mac, find it using Spotlight, use the Finder to go to /Applications/AppInventor/commands-for-App, and double click on aiStarter. On GNU/Linux, this program is in /usr/local/bin. You should be able to start it by typing aiStarter from a terminal. More help with aiStarter...

On Windows, App Inventor cannot connect to the device, and the command window for aiStarter shows:
The system cannot find the path specified. Problem checking for devices: status 1.

To fix this, reinstall the setup software, following the directions at
How to update the App Inventor setup software.
Be sure to do uninstall before reinstalling, and to perform the installation from an
account that has administrator privileges.

The AI Companion

Google Play will not download the AI Companion app to my phone. Is says that the app is not compatible with my device.

Google Play is often overly conservative about whether an app is compatible with a given device. This is especially true for tablets. The AI Companion should be compatible with Android operating system version 2.3 and later. If Google Play refuses to install the Companion, try using the QR code at the right on the page Connect your Phone or Tablet over WiFi , which links directly to the APK file.

I cannot find the MIT AI2 Companion App on the Google Play Store.

This is probably the same issue as above, especially on tablets. If you cannot access the MIT AI2 Companion App via the Google Play Store, you may download the APK file from this page and install it directly onto your phone (note that to directly install, you will need to allow installation of non-market apps in your device's system settings). This can also happen if your have content filtering on your Google Play account. You'll need to allow "apps for everyone" on your account in order to see the Companion in the Play Store.

Installing device drivers

I ran the App Inventor Setup installer on Windows, but the phone device drivers do not install.

There are multiple reasons for this, and we're trying to track them all down. The Windows driver installation instructions in the App Inventor documentation contain our best advice, and we'll keep those current as we get more information from users.

Note that the drivers included in the App Inventor Setup software do not work on all Android devices, and you may need to get drivers from the manufacturers. See the Windows driver installation instructions for advice, and check the App Inventor Forum to see if others have had similar issues with the version of Windows and the particular device you are using.

Also, the driver issues around App Inventor are the same as for the Android SDK in general, so doing a Web search for driver issues around the Android SDK may also be worthwhile. It also might be worthwhile to search the Android Beginners Google Group and the Android Developers Google Group.

Using the Blocks Editor and loading projects

My Blocks vanished from the Blocks Editor.

They may have scrolled off the window. Try moving the scroll bars. A way to move the scroll bar even more than it allows is to drag a block to the bottom or top of the scroll bar, release, and repeat.

The Blocks Editor won't connect to the phone or media files don't show up on the phone.

There are several possible causes for this, depending on the model phone you are using. Causes include (1) the settings on your phone and (2) interference from other applications running on your phone or your laptop. Take a look at steps 5 and 6 on this page for some things to try.

I'm using Firefox and I get a message about being unable to access project definitions.

If you are using Firefox and have the "noscript" extension installed, you'll need to disable it or else you'll see errors saying that the system cannot access your project definitions. Other tools and system configurations that restrict access to your computer (e.g., firewalls) may also interfere with App Inventor. You should check for these if you encounter errors about reading definitions or connecting to the phone.

Connecting the phone over wifi

I'm using wireless and the phone won't connect to the blocks editor.

Try the following steps to troubleshoot your wireless connection.

  1. Try to reach from your computer.
  2. Try to reach from the phone itself.
  3. If the steps above both work, try using the "ping" command to ping to the IP Address of the phone (displayed by the MIT AICompanion in its startup window). If you are using windows, type "ping" + *IP address of the phone* in cmd.exe window, if you are using Mac or Linux, type "ping" + *IP address of the phone* in the terminal window. For detailed instruction see
  4. If all of these steps succeed and Wireless App Inventor still doesn't work, then there may be a firewall between the computer and phone that is blocking ports 8001 and 9987. If you have a "telnet" program, you can attempt to telnet from the computer to the phone on these ports. If the connection won't complete, then there is likely a firewall in place that is blocking connections to the phone.

I installed the MIT AICompanion App before and it doesn't work now.

You must use the latest version of the MIT AICompanion App. If you attempt to use an older version of the Companion App with App Inventor, you will be prompted to update it.

I followed all the wireless instructions and my phone is connected to WiFi, and I still cannot connect to App Inventor via WiFi.

If you have trouble connecting using these wireless instructions, make sure your phone is using WiFi and not the cell network. On some devices and in some locations, even with WiFi enabled, the phone continues to use the cell network for Internet connectivity. If this is happening to you, you can disable mobile networking (cell phone carrier based Internet connectivity) from your device's Android settings menu. More information about how the WiFi connection works.

Communicating with the device

App Inventor says: You must be connected to the companion or emulator to use "Do It".

This message means that App Inventor believes that it's not connected to any device. If you are using the USB cable, first check that the phone is plugged in. You can also check the connection by using the Connection Test Page. Once the phone is connected, stop the Companion software on the phone and try connecting again. If this does not work, or if you are not using USB, try the solution shown under "App Inventor says: Network Error Communicating with Companion."

The phone (or emulator) shows a notice -- Security error receiving blocks from browser.

A likely cause for this is that the browser loaded a new project and the Companion didn't recognize that. (Perhaps the phone was unplugged?) Reset the Companion by using the menu key (on the emulator) and select "stop this application." Then reload the browser page, and try connecting again.

The Companion started to run, and then said "Connection error."

This can happen if App Inventor tries to connect and start the companion, and the companion is already running on the device (perhaps from previous project). Go to the running Companion app, press menu, and choose to stop the application. Then try reconnecting again. If this keeps happening, try rebooting the device.

Using USB after using the emulator

I was using the emulator and now I can't use the USB cable.

App Inventor sees only one connected device at a time. If you were using the emulator, you'll need to quit the emulator program before you can connect phone with USB.

Running apps on the phone

I was developing an app and it crashed on the phone.

From the Connect Menu click "Reset Connection" and then click "AI Companion" to restart. Ask for help from other users in the App Inventor Forum.

My phone doesn't seem to match what's in my program.

First try clicking the Designer button then click back to the Blocks button. Sometimes the app showing on your phone is lagging behind what is in your browser, and needs to be updated on your phone. Switching between these two screens causes a refresh to happen.

I was developing an app and I unplugged the phone, and the app disappeared from the phone.

It's supposed to disappear. If you want to use the app when the phone is disconnected, you'll need to package it and download it to the phone.

The code size for the apps I create is very large. Even the simplest apps have apk files that are larger than a Megabyte.

App Inventor apk files are in fact very large. We're working to reduce their size.

My app causes a virus warning.

There is a known issue with certain virus protection software, in particular the "Dr. Web" anti-virus app. Any app that uses the texting component (SMS) will generate the virus warning "android.smssend.origin.247". This is a false positive virus detection that you can safely ignore.

Testing apps with multiple screens

I'm trying to test my app that has multiple screens and it's not working correctly

Apps with multiple screens must be packaged and sent to the phone to test. If this is a problem for you due to wifi or other issues, follow these instructions:

  1. Download the free app called ES File Explorer from the Google Play Store on your Android device.
  2. Use the App Inventor Designer Window to download the app to your computer. (Your Blocks Editor Window must be launched for a successful package).
  3. Connect your Android device to your computer as a USB Device.
  4. Using your computer, navigate to your file manager, find your device, and double click to navigate to its Download Folder.
  5. Drag and drop your app's .apk file from the Computer's Download Folder to your device's Download Folder.
  6. On your device, launch the ES File Explorer App. Using this app, you can then navigate to your tablet's Download Folder and double click on your appinventor app to launch it!

Loading and saving projects

App Inventor says there's an error and it cannot load my project.

This might be a transient error coming from App Inventor's link to the cloud storage system. Try again after waiting a minute and see if the problem recurs. If the problem does recur, then there is probably some problem with the project file itself. Please file an issue report telling us about it. Attach the project source (aia file) if you can.

Working with sounds and images

I set the image property of a button (or other component) to an image file, but nothing shows on the phone.

There are several possible causes for this, so there are several things to try:

  • Make sure your phone has an SD card and that the SD card is not full. App Inventor uses the SD card for temporary storage of images, and the phone needs to have an SD card in order to run App Inventor.
  • If connected via USB, make sure your phone's USB connection mode is not mounting the SD card. For example, on the Droid, you should set the connection mode to "charge only".
  • If you get an error message about external storage, you'll need to check that your phone is not set for Mass Storage mode: Tap the Home button to go to your phone's Home screen, then Tap the Menu button, then tap Settings, then tap Connect to PC. Tap Connection Type and choose "Charge Only". Make sure that other choices are not selected. It is especially important that choices "Disk Drive" or "Mass Storage" are NOT selected (these words vary by phone and Android Operating System version).
  • Try unplugging the phone and plugging it back in. Followed by clicking on the "Connect --> USB" menu in App Inventor.
  • If that doesn't work, try packaging and downloading the app. Start up the downloaded app, and see if the image appears on the phone. If the image does appear, then you'll have to continue developing without the image showing on the phone. You'll see your app in its full glory only after you've packaged and downloaded it, not while you're developing the app live. Please ask about this in the App Inventor Forum.
  • If your image does not appear in the packaged app either, then you should suspect that there is something wrong with the image file. Perhaps it is not really an image file: Try examining the file with some graphics software. Perhaps it's not an image in a format that App Inventor can process: App Inventor can handle JPG, PNG, or GIF. Maybe the file is too large: try using graphics software to cut its size down to less than 300K.
  • If none of these things work, try asking for help in the Forum.
  • Tip: You can sometimes see system complaints about the phone running out of storage by using the Android Debug Bridge (adb) to examine the Android system log.

I set the source property of a Sound or Player component, but there's no sound when I tell the phone to play.

If you are working with the phone connected to the computer, make sure the phone really is connected. Try using "Do it" on a few blocks, including the block that tells the component to play. Also make sure the phone's media volume is not turned down!

If this doesn't help, try some of the same things as with images, above. Watch out for running out of storage. (See information on media in App Inventor.) And make sure the audio file is a format the Android (and hence App Inventor) knows about. MP3 and PCM/WAV files should be OK, but there may be issues with other formats. See for a list of supported media formats. Warning: Not all WAV files are PCM/WAV.

Text-to-Speech is not working on my phone (or tablet).

First, check to make sure that the volume on your device is all the way up. Also, be sure you've got something typed into the dark pink text block that should be plugged into the purple TextToSpeech.speak block. If that text box is blank then you aren't telling the device to say something.

Then, if you still don't hear anything, check to make sure your device has Text-to-Speech installed. It is supposed to be standard on all Android devices. To check if you have TTS on your device go to Settings -> Controls -> Language and input -> Text-to-speech options. You should see Google Text-to-Speech. If it's not there you can most likely install it from the Google Play Store. If you are working in a language other than English, you'll need to install the Google Translate app:

Then, you need to have the language package for the language you wish for: settings->language + input -> tts output then: select google tts (if it's not already selected)

Hello Purr does not work on my Lenovo A1 Tablet -- the meow.mp3 file won't play.

Change your blocks to use the Player component instead of the Sound component.

Building projects

When I try to build my project, it fails with "unexpected problem generating Yail".

This error occurs if building the project fails at the very last stage. This error message is a catch-all that covers "unexpected" errors where App Inventor hasn't provided a useful error message.

There are several situations where this error has been observed. One is with large projects that have multiple screens: The individual screens build correctly, but the system runs out of space in putting all the screens together at the final packaging. Another situation is where the project file is corrupted, for example by the user unzipping it making an edit and then re-zipping it. This can lead to spurious files being included in the new zip file, which confuse the compiler. Another might be bad names for figures or other assets, that can trip up the compiler.

If your project gets this error, think about whether there could be causes like the two listed above. If that doesn't help, try asking in the Forum: You'll need to attach your project source so that someone can try to diagnose the problem.

When I try to build my project it fails with "Server error: could not build project".

This could be the result of a transient storage failure, so try again. If the problem persists, this is a similar issue as for "unexpected problems generating Yail." One program issue that causes a build failure is if your program contains two event handlers for the same event with the same component (for example, two Button1 when-clicked definitions). This is a known bug in App Inventor that will be fixed. Until then, if your program build fails, check to see if you've defined multiple event handlers for the same event.

When I try to install my project on the phone, I get the error "unable to parse package".

One possible cause for this error is that your phone does not have enough free memory to install your app. Also, when an app is installed it is expanded from the APK file: the installation requires about 3 times as much space as the size of the APK.
Look under your phone's settings to see how much available storage you have. You might need to uninstall some older apps to create the necessary space. Android installs App Inventor apps in its internal memory, so even if you have space on the external memory (SD card) you might still have problems. The "unable to parse" error can also occur when the APK file is too large or includes extraneous files. Check the files listed under Media to see if any were included by mistake, or if there are any that you don't need.

Keystores and Signing of Applications (".apk" files)

I'm seeing the error [INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES] when I try to download my app to my Android device

If you get this error message you most likely are trying to reinstall an app on your device that you have previously packaged and installed with a different App Inventor service. For example, you might have packaged the app originally with the Google App Inventor service and now you are trying to re-package with the MIT App Inventor service, or with a service that someone else is running. If you don't have any data associated with the app on the device (e.g., in a TinyDB) the easiest solution is to remove the app from the device and then install the new version. If you need to preserve the data associated with the app, and you have a copy of the keystore that was used to package the app that is already installed, see below for how to upload the old keystore to the new service.

What is a keystore and why might I want to upload or download one?

Every Android app (".apk" file) needs to be signed with a key belonging to the user who creates the app (see for lots more information on signing apps). App Inventor generally handles this for you behind the scenes, so that most users don't need to think about app signing most of the time. However, you might run into a situation where you need to know about app signing if you move between different App Inventor services and you want to reinstall an application that was built on a different service while still preserving its local data. App Inventor keeps the key used to sign your apps in a file called a keystore. When you first start using an App Inventor service it creates a new keystore for you and uses that to sign any apps you package on the service. If you move to a different App Inventor service and want to keep using the same keystore to sign your apps (to avoid the inconsistent certificates problem mentioned above), you will need to download (or otherwise obtain) the keystore from the old service and upload that keystore into the new service. Options for downloading and uploading keystores can be found in the My Projects tab, under the More Actions menu. Note that the same keystore is used to sign all of a user's projects in a given App Inventor service, so you cannot designate one keystore for some apps and a different keystore for other apps.

How can I get the keystore that was used to package my apps in the original Google App Inventor service?

Most users of the original Google App Inventor service can find a copy of their app source zip files, as well as the keystore that was used to package their apps, in their Google Docs accounts:

  • In your browser, go to
  • Search for
  • Download the zip file by clicking on Download under File.
  • Unzip the downloaded file and you will find a directory called keystore containing a file called android.keystore. This file contains the keystore that was used to sign the apps for that App Inventor account on the Google App Inventor service.

We detected errors while reading in your project

I received the message "We detected errors while reading in your project" when starting App Inventor or Switching Projects

The copy of your project received by your computer differs from the version sent by the MIT App Inventor server. This is most likely caused by a server or filter, not controlled by MIT, located between our servers and your computer. You should check with your local computer/network technicians. You may be able to find help in the MIT App Inventor Forums.


App Inventor says to "check the debugging messages." Where are these?

This is an especially unhelpful error message that will be fixed in the next update to App Inventor. It is generated when App Inventor cannot complete the compilation of a program. The most common cause for this is that there are two event handlers for the same event with the same component (for example, two Button1 when-clicked definitions). Check your program for this and try again. If that is not the problem ask for help in the forum, and include the name of your project.

I'm just lost!

Ask other users for help on the App Inventor Forums.