computer sparse bundle is already in use error

No need to reboot... Should work if you simply change the password on your Time Capsule via the Airport Utility (in your utilities folder). Alas, this is just another example of Apple releasing buggy (crappy) software and then not fixing a big problem.

I too am days old owner of a new imac 27" and 2TB time Capsule running OSX ML 10.8.2 and Airport utility 6.1 after 20 odd years of PC ownership and have spent the last 24hours trying to sort out this backup scenario - I thought apples just worked?

The first backup I performed pretty much out of the box (so less than15GB) worked ok albeit it took close to 10 hours???. I then tried to copy and past the backup files to an external Western Digital portable HDD as a backup - that didn't work as the TC kept dropping out. Then I tried doing another timemachine backup directly to the WD HDD which worked fine. When I tried to swap back to the Time Capsule as the backup disk problems started hanging trying to find the disk, sparse bundle already in use etc. I tried all sorts of fixes outlined in these discussions, ejecting all, restarting both TC and imac, resetting TC password, turning all off and on multiple times. I didn't go so far as reformating or re-installing anything but after hours of frustration the only thing that finally worked was deleting the com.apple.TimeMachine.plist as described in the link below;

http://pondini.org/TM/A4.html

I did that, re-selected the TC as the backup and Bingo...worked like its supposed to. It made a new backup in addition to the original one.

Hope that helps others trolling through these forums with similar issues like I have been...

As a note from auto backup trials it also seems vitally important that the "Time Machine Backups" volume is not mounted and showing on the deskptop for the backups to successfully work. Seems to work if the TC "Data" volume is mounted but not "TM BAckups"

If you are running Mountain Lion and getting this message when trying to backup, try this:

Open AirPort Utility (If you are in Mountain Lion this will be 6.0 or Higher)

Select you Time Capsule

Select the Disk Tab
Deselect "Enable File Sharing"

Click OK Let the Time Capsule Re-Boot

Go Back into AirPort Utility and re-select "Enable File Sharing" and let it Re-Boot again.