OK, I have a rather straighforward setup: In my office at work I have a Airport Extreme that has a 500GB USB hard drive called Chimeara. It is the only disk I've ever had plugged into this machine with that name. I have Time Machine set to backup to this disk. Four times in the last year, I've received the "The identity of the backup disk has changed since the previous backup." When I select "Use this Disk," Time Machine starts a brand new backup, ignoring the previous ones. So now I have four old backup bundles, and Time Machine wants to start a new one. Not only am I out of space on the disk (and don't want to delete previous backups), the data I have backed up is fragmented by date making looking for a specific file a major pain in the rumpus. Anyone have any guidance on what is causing this?