Some Time Machine users who are backing up to a Time Capsule drive may experience a problem where they can neither back up nor enter time machine.
Apple Discussions poster Shooter Mike writes:
"This is the second time I have experienced the following problem with Time Machine. After 2 months of backups it gets to a point where backups fail and I cannot enter time machine."
The solution so far has been for users to delete the sparsebundle image file on the time capsule and restart the backups, which defeats the point of a backup system to an extent. When users have done this the backups work again as they should, but the problem seems to reappear after a while.
This problem may be coupled to the Time Machine drive being mounted in the Finder at all times. When Time Machine backs up to network volumes, it first mounts the remote disk image and then unmounts it when the backup is complete. If the disk image does not get properly ejected then this could make Time Machine think the disk image is already in use. Unfortunately users may not be able to eject the mounted image file, and Mac OS X may give an error stating the drive is "in use".
Sparsebundle images are relatively new in OS X, since they were introduced with Leopard to enable efficient network backups with Time Machine. As such there may still be a few bugs with how they are handled in certain situations. In the past users have reported problems with sparsebundle resources being in use by other users, which prevented other users from accessing the images. It appears a similar "image resources" problem could be involved with this issue since users have been able to fix the problem by manually disconnecting all users from the Time Capsule.
Fix: Disconnect all users from the time capsule To manually disconnect all users from the Time Capsule, open the Airport Utility and choose the Time Capsule device on the list to the left. Then click the "Manual Setup" button and select "Disks" in the resulting window. Then click the "Disconnect All Users..." button, quit the utility, and reattempt the backup.