I have a 200 GB hard drive in my iMac and a 320 GB external for Time Machine. I just started getting this bug, I think since I updated to 10.5.2. Time Machine starts backing up as usual, then an error message pops up saying "The backup requires 8.2 GB but only 12.3 GB are available." I have no idea what to do now. Isn't TM supposed to automatically delete old backups when the drive is full? There isn't anything in the preferences to enable/disable it.