I get this error on Android Studio:
Project was created in Android Studio from scratch, and it was working fine.
What change I made (if I recall correctly), was about a popup dialog, like "
Android Framework detected
On Android Studio v0.8.2 clicking on
Sync project with Gradle files button solved my problem.
Thanks to the comment of jaumard. If the
Sync project with Gradle files it's not visible you have to open the Gradle panel and click sync icon on top the toolbar.
Hope it helps :)