As per this answer, I tried to add MoPub as a standard project to my Android project by using Build Path > Link Source. This put a mopub-sdk folder under my project folder, and now I can't delete it. I get the following error message:
An exception has been caught while processing the refactoring 'Delete'.
Reason: parentPath must not be null
I actually added the MoPub SDK twice. The first time, I named it mopub-sdk, removed it from the Build Path, and saw that the folder in project explorer was still there, tried to delete it, and then got the error message.
The second time, I wanted to test if having removed the SDK from the Build Path caused the problem, so I tried to re-add as a Link Source, got a naming conflict error, and then named it mopub-sdc instead. Trying to delete from Eclipse's project explorer first still caused the error, only this time it included the options "Click 'Undo' to undo all successfully executed changes of the current refactoring" and "Click 'Abort' to abort the current refactoring."
Any ideas? It might be notable that both folders have [Ignored] next to them.