Why Android Gradle preDexDebug “Source and destination must be different” build failed?

Question

I have an Android application built with Android Studio 0.8.1 and facing the issue:

Error:Execution failed for task \':app:preDexDebug\'.
> java.lang.Ille         


        

Answer 1

Delete the build folder in your project and invalidate cache in android studio, restart android studio

Answer 2

The answer was just to clean the project. I was having same problem for some time.

Build -> Clean Project