In most cases, App Inventor should be able to locate the Setup software on its own. If you have installed a previous version of the App Inventor 2 setup tools, you will need to uninstall them before installing the latest version. Installing via a non-administrator account is currently not supported.
You must perform the installation from an account that has administrator privileges. On Windows, App Inventor cannot connect to the device, and the command window for aiStarter shows: The system cannot find the path specified.For Windows users, we recommend using either Chrome or Firefox as your browser for use with App Inventor. You should be able to start it by typing aiStarter from a terminal. On the Mac, aiStarter should start automatically, so Mac users should not have to worry about this. On Windows, there should be a button on your desktop that starts aiStarter. If it is not running, you'll get an error message that says so. Whenever you want to use the emulator or the USB cable, you need to make sure that aiStarter is running. It provides communication between different parts of App Inventor, including the part in your browser. The aiStarter program is installed on your computer with the App Inventor Setup software.
MIT App Inventor 2 - How to Download Your App on Your Android Device
See the instructions at the How to update the App Inventor setup software page. App Inventor should resume connecting automatically. Unplug the phone, wait 5 seconds and plug it in again. Then try connecting to the emulator again. Use shift-reload to also reload the cache. To fix this, reload the App Inventor page in your browser. Some people have observed a problem where the app runs on the emulator, but images do not appear. If this does not help, see the steps under Emulator Connection Help Guide.
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. The most common cause here is that App Inventor setup software needs to be reinstalled. This message means that App Inventor believes it's connected to the emulator, but it is getting no response from the AI Companion software that should be running there.
Try resetting the Companion and reconnecting. In addition to the troubleshooting suggestions shown here, you can check out the page for General connection help. Still not working? See How to update the App Inventor setup software. Follow the instructions carefully, including the steps of rebooting and uninstalling. If that doesn't fix the problem, reinstall the setup software. If you are having trouble with the emulator or USB, first try visiting the Connection Test Page to verify that aiStarter is running and that you have installed the latest version of the setup software. The Companion can't update if that address is being blocked. That is where the new version of the Companion can be downloaded. The Companion within the Emulator display an errors message when I attempt the update. Be sure to follow the instructions about uninstalling and reinstalling, including the rebooting steps. Go to our test page to verify your setup, and install the latest version if necessary. If you are using the emulator and you see this message, it most likely means that you are using old setup tools.