Unlock.exe clears orphaned locks by specifying the lock (from the error message) on the command line.
VSS uses different mechanisms to implement mutual exclusion within the database. (This has nothing to do with checking out files). If VSS stops unexpectedly, it may leave some of these mutual exclusion locks behind. The next time VSS tries to access the protected records, it reports an error.
Syntax
UNLOCK lock
Lock is the lock name displayed in the "time-out locking" error message.