Specific Error: Time Machine could not not complete the backup, .sparsebundle is already in use
I began backing up my Macbook Pro to my Synology NAS since I didn’t want to lug around an external disk with my laptop. It worked seamlessly for a week until one of a few things happened that caused the backup to fail in mid-backup. I either powered off the system or the system went to sleep during the backup.
Upon restarting the computer, I received an error message when Time Machine once again started to do it’s thing. The message read: Time Machine could not complete the backup, .sparsebundle is already in use. When I searched the error, I found easy solutions for people using an external drive while connected to an Airport Extreme and backing up to a drive attached to that. It involved simply killing the user sessions that were associated with the drive and in a few cases rebooting.
On the Synology NAS, using DSM, there is also a simple solution. Log into the NAS as an admin. In the lower right corner of DSM there is a list of the current sessions. Click on the icon to the right of the session and “Kill connection” on the session that Time Machine is using. If you made a specific account for Time Machine it will be easy to find, otherwise you may need to kill multiple sessions flagged with AFP as the protocol. See below for the part of DSM you are looking for.
Keep in mind that you will only see this window if it is not collapsed. Click the up arrow in the lower right hand corner to show it if it is hidden. You will also only see the connection if the window is big enough to display it since System Health, Resource Monitor, and Recent Logs show above the current connections.
Hope this helps someone out.