IntelliJ IDEA 12 duplicate class R.java and BuildConfig.java

Question

I use Eclipse for android development and trying to use IntelliJ. I have successfully run the application once. But now, I couldn't seem to rebuild the example Hello World application. What am I missing here? The R.java is not rebuilding anymore. Here is a screenshot of the errors.

And here is my setting

Answer 1

This happened to me because I've marked source folders incorrectly. Under project settings once you click on particular module, Just check whether you have Mark any additional folders as source folders. Check the screenshot, By default it should be something like below, All mark as buttons should be unchecked

By mistake I've checked Mark as: "Source" button and I got this error. Just uncheck it.