I keep keeping an error when trying to use Time Machine: "Last Backup failed. Error while creating backup directory." I've tried restarting my computer, unplugging and replugging in my hard drive, ejecting my hard drive, and unplugging my hard drive from the wall and replugging it in there after 30 seconds. No go. I'm using a WD MyBook. The last successful backup was about 4 hrs ago. I can still access all the old backups with no issues off the hard drive. Any ideas?