If the AdminGem is not running, then garbage collection steps from previous operations cannot complete. The error message returned from the markForCollection operation does not indicate the nature of the problem, it reports the lock was denied with the reason "vote state is doneVoting".
You should normally leave the AdminGem running. Start the AdminGem using
System startAdminGem
This can be done as part of the MFC sequence; executing it when the AdminGem is already running does not cause problems.
Last updated: 3/25/16