It's a bug in Windows. It usually happens when you try to empty the Recycle Bin while a file or directory is in use by a service or program. Once the file or directory becomes unused by the service or program, Windows will empty the contents of the Recycle Bin while leaving the full Recycle Bin icon. When you try to empty the Recycle Bin again Windows doesn't find anything so it'll ask you to delete the root directory, this being WINDOWS. However, if you notice, there are 0 bytes worth of information and no WINDOWS directory in the Recycle Bin. Nothing happens if you empty the Recycle Bin. Also, a user logoff and then login will refresh the Recycle Bin icon.