This is not something I do, although I've done this once or twice in the early days of Time Machine. So here's what I remember:
Simple solution (from Bob Timmons):
1. Make sure that no other Macs are backing up the Time Capsule at the time 2. Pull the power cord from the back of the Time Capsule 3. Count to ten 4. Plug the power cord back into the back of the Time Capsule |
Now I also seem to recall mounting the "bad" sparse bundle by double-clicking on it. Once mounted it will appear as an ordinary disk. Use Disk Utility to repair the disk (do not repair permissions.) Then eject the mounted image and see if you can once again use it.
If this is all a big failure, then I think you are left with using Time Machine to place that particular computer's disk into the Exclude list. This should delete it so you can start the backup from scratch.