I am getting this error trying to sync 2 external backup drives on Windows.
Short Version: 10216895 [main] DEBUG org.apache.commons.vfs2.cache.SoftRefFilesCache - putFile: file:///F:/Repositories/Xbox360Game
java.io.IOException: Could not list the contents of "file:///F:/S1M0NE" because it is not a folder.
I have determined that this error is due to file system permissions. HOWEVER, this error doesn't pop for several minutes, and HALTS EXECUTION. The program should be changed to allow the user to choose to continue execution on an error like this. It would not hurt either to have it recognize the problem of lacking permissions, and skip over any files and folders where access is denied.
Incidentally, Run As Administrator worked for me, but that won't help for everyone.