Session 'app' error while installing APK

Question

I am having difficulty importing a project written on Android Studio 1.1 into Android Studio 2.1.2. I keep getting this error whenever the gradle is building before testing

Answer 1

This is a terrible problem, i have facing it so much time, First of all when you run on emulator or real device please make sure that it is not show device is offline in Android monitor, see picture below due to bad cable connection device is showing offline, so make sure first that it is online.

If it's Okay then clean your project and Rebuild your project. You can do it from Build -> clean project / Build-> Rebuild project

Still problem occurs then try to Restart android studio. This is generous error happens due to above cases.But i solve it this way as described.