Nor can I! And there's a big giant "WTF" coming, although in a good way so far.
So I got home from work and booted from my 10.5 install disc to verify all of the drives in attached to the machine. All verified fine. Rebooted into OS X, dragged the SuperDuper sparsebundle into Disk Utility and clicked Repair, it said it passed verification. So I clicked Open in the toolbar.. and it mounted?!
As I type this Disk Utility is busily restoring the sparsebundle quite happily to a spare partition. WTF! Not that I'm complaining, mind you!
I'd just love to know wtf happened.