Access revoked, Backup Set in use

Symptoms

Various activities may report the error message "Access revoked, Backup Set in use". This message is generated on the DS-System side, but may be reported on the DS-Client side as well.

Cause

Cause (1): A lower priority process using the backup set was stopped, in order to give a higher priority process access to the backup set.
Cause (2): "Access revoked, Backup Set in use (Backup Process)" in scheduled backup.
Scenario (a): If a scheduled backup lost connection to DS-System, it will retry 3 times in 5 minutes interval. If DS-System is still processing this backup set and DS-Client re-establishes connection to DS-System and resume the backup, this error may shown. 
Scenario (b): A backup finishes with BLM enabled. DS-System is still busy with archiving old generations of this backup set. If at this time the backup will be started again, this error will be reported.
Cause (3): A BLM archiving activity was interrupted, so there is a lock placed on the backup set until the archive request is completed or deleted.
Cause (4): An activity waiting to get the lock for a backup set (that is already in use) was interrupted or times out, but shortly after that the lock is released and then the lock is assigned to the activity in queue. Because of this, the lock is assigned to an activity that actually isn't running anymore. [This issue is less likely to happen in DS-System v9.0 and above, due to some additional checking being done before assigning the lock to the new activity] 

Workaround

Resolution (1): Try again after the other activities finish or stop the other activities.
Resolution (2): No action needed. Just wait for the BLM activity to complete and restart the backup activity.
Resolution (3): From DS-Operator > BLM > Active Archive Requests, locate that activity and either "Delete" it or "Start" it again, so it will complete successfully.
Resolution (4): Restart the DS-System service in order to release the lock.