“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

Try to right click on the project and choose Open Module Settings. Then go to the Sources tab in your module, find the src folder, right click on it and mark it as Sources (blue color).

EDIT: There is no sources tab in later versions of Android Studio, but you can edit the build.gradle file instead: https://stackoverflow.com/a/22028681/1101730