Session 'app': Error Launching activity

I also faced this issue after I updated to AS2.0. I found that it is because of the instant run enabled. So my solution is to disable the "instant run". and it worked. To disable "instant run", you can go to Preference Dialog ( May be Setting dialog on Windows), then select Build, Execution, Deployment > Instant Run, and uncheck all the checkbox to disable Instant Run.

This is my temporary solution and it may help you. Later, I'll find a better way to this issue.

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update by 2016/06/06

A better solution instead of disabling instant run. Remove the .idea folder and .gradle folder, then click button Sync Project with Gradle Files (or through the menu File -> Sync Project with Gradle Files), after this process finished, you are able to run your app as normal.

Good Luck~

If you are using Android 7.0 and above it is likely that the app was installed in two places (Guest and Admin) and you only Uninstalled it for only one user and that is causing problems.

To solve that, go to: Settings -> Apps & Notifications -> See all Apps -> find the app you are trying to install.

Then click the menu on the top right corner and select Uninstall for all users

Run Your App from Android Studio it should work.