Currently Being ModeratedMay 9, 2012 9:42 PM (in response to Alex Johnson2)
I know this will sound brutal, are you able to back up your stuff to another drive and then do an erase/format of your Time Capsule disk? Remount the disk and let Time Machine reestablish itself. You would then know if the backup itself was corrupted in some way.
Currently Being ModeratedMay 13, 2012 1:22 PM (in response to RRFS)
I was about to try this, but the problem was solved - by updating to ML DP3. Time Machine was able to report more specifically a UUID mismatch - which was strange as there had been no hardware changes:
Event store UUIDs don't match for volume: MacBook Air
Deep event scan at path:/ reason:must scan subdirs|new event db|
Found 360330 files (16.14 GB) needing backup
21.25 GB required (including padding), 17.99 GB available
Deleted backup /Volumes/Time Machine Backups/Backups.backupdb/MacBook Air/2012-05-06-132701.inProgress/36723EA8-68F9-4519-A71B-426EEEE06222 containing 896.2 MB; 18.88 GB now available, 21.25 GB required
Deleted backup /Volumes/Time Machine Backups/Backups.backupdb/MacBook Air/2012-05-06-132701.inProgress/73A7127D-0521-46C0-AD8F-F7C6B6621F86 containing 4 KB; 18.88 GB now available, 21.25 GB required
Removed 2 expired backups so far, more space is needed - deleting oldest backups to make room
Deleted backup /Volumes/Time Machine Backups/Backups.backupdb/MacBook Air/2011-10-08-102105 containing 10.75 GB; 29.63 GB now available, 21.25 GB required
Deleted 3 backups containing 11.64 GB total; 29.63 GB now available, 21.25 GB required
Backup date range was shortened: oldest backup is now 15 Oct 2011
Copied 2.7 MB of 16.14 GB, 106708 of 360330 items
Copied 5.6 GB of 16.14 GB, 360849 of 360849 items
Bulk setting Spotlight attributes failed.
Copied 394370 files (8.46 GB) from volume
Upshot is that after many hours it's back, and the sparseimage has been verified.
If it's of any use to anyone finding this, I would say that the solution seems to have been a Mac OS reinstall - which is counter-intuitive, but if all else fails, give it a go!