“Default Activity Not Found” on Android Studio upgrade

Question

I upgraded IntelliJ Idea from 12.0.4 to 12.10.

Now all the modules in my Android project give the error:

Error: Default Activity Not Found

Answer 1

If you see that error occur after upgrading versions of IntelliJ IDEA or Android Studio, or after Generating a new APK, you may need to refresh the IDE's cache.

File -> Invalidate Caches / Restart...