this is almost impossible to reproduce here locally. It is also a concurrency issue on windows. The problem is: if there is already something else trying to create the file, Windows generally responds with "Access is denied".
I think we should catch IOException in the obtain() method and handle this in a similar way like in NIOFSDir (return false, so lock was not aquired successfully).
I will provide a patch after trying to reproduce this on windows (by making filesystem and cpu busy).