Trouble repairing a corrupt Time Machine sparsebundle on Synology NAS
I got this error message when I tried to restore from my Synology. But I found this

http://thefunkstop.com/fix-corrupted-time-machine-backups/

Turns out that that the "Time Machine user" was never disconnected when my last backup was interrupted. I had to manually disconnect the user and then everything worked when I tried again. But I think it should work by restarting the NAS as well.
I hope this can help...