There is a very good thread here
On page 4, user Hoppah discovers that his Time Machine (TM) backups go corrupt if they occur simultaneously with "RAID scrubbing." The RAID scrubbing is a function of the network application server (NAS) run periodically to check consistency.
Hoopah used the TimeMachineEditor utility to ensure that TM backups did not occur at the same time as the RAID scrubbing. That solved his problem.
There is a post from a user Christof Birkenmaier, also on page 4, about how to mount the disk image of the backup and delete the portion of the backup causing the problem. It is a very ugly fix that requires editing the TM record of its state. Scary.
A blog entry at
explains loading the TM disk image with the Disk Utility to repair it. If that fails, it explains a command line method to run a file system check on the attached, but not mounted TM disk image.
Elsewhere in the thread first referenced above, from discussions.apple.com, on page 3, there is information about how to look at log files to spot the errors.
It appears TM backups may be corrupted if the network connection is interrupted during backup. You pack up and leave your house while the backup is running. That pulls the plug on your wireless connection to the backup device. Nasty thing to do to TM.
I have decided to run TM manually, when I know it won't get interrupted, and when I know the NAS is not doing RAID scrubbing.