After the Android Studio 2.0 update while the gradle build finishes I get this :
Session \'app\': Error Launching activity .
It prevents the app from starting
Just Run --> clean and rerun , In my case it helps. Prompts automatically like following message
Run --> clean and rerun
would you uninstall already installed activity with same name
if activity is already installed first uninstall it and make project ready after installing app.