From: https://www.veritas.com/support/en_US/article.TECH67698

HKLM\software\Symantec\Backup Exec for Windows\Adamm\Disable Library Door Lock

From: http://serverfault.com/questions/259324/how-to-backup-symantec-backup-execs-catalog

  look at the catalog settings in the Options menu, under "Settings" and "Catalog", and see 
  where the catalogs are stored

From: http://serverfault.com/questions/259324/how-to-backup-symantec-backup-execs-catalog

  I wonder if your catalog retention period is set to an exceedingly long period, regular 
  catalog pruning operations aren't taking place, or something has gone crazy. I'd have a 
  look at the catalog settings in the Options menu, under "Settings" and "Catalog", and see 
  what the retention period looks like. Do you see any odd "alerts" re: catalogs? 

From: http://pcloadletter.co.uk/2012/02/08/backup-exec-tapes-refuse-to-catalog/

  The workaround was was to select the problem tapes in the Media tab, associate them with 
  the Retired Media Media Set, then right-click and delete them from the media view. This 
  removes any mention of that media from Backup Exec’s database. Then rescan the autoloader’s 
  slots in the Devices tab, and run an Inventory job on them all. Finally, run the Catalog job 
  once again – then it works.

From: http://www.symantec.com/business/support/index?page=content&id=TECH83082

  To manually take a backup of a Backup Exec database, use the Dump database option of BEUtility. 
  The database file is dumped to a file on the hard disk and is maintained until the next dump operation.