TimeMachine Backup failed with error 11: 11
it's time to battle an annoying TimeMachine problem. A short foreword I'm running a FreeBSD solution with netatalk and avahi but suddenly it stops with the above message: Backup failed with error 11: 11. It's recommending to repair the backup drive but well there's no hardware error. So I went on the search in the shallows and found the solution: just delete any existing .inprogress files and then you're good to go.
What I specifically did was to navigate to eh /Volumes drive and mounted my .sparsebundle file
hdiutil attach somename.sparsebundle/ -noverify -noautofsck -readwrite
Afterwards I moved to the newly created Time Machine related folder in /Volumes and find the .inprogress file and delete it. Afterwards just restart the Backup. It should work now.