Incase if you want to manully remove tape from the Library (without using import and export withing backup exec and running lock unlock operation ) you can proabably schedule a script to stop Backup exec services and then later start the service again . Also you can check the option to run inventory when you restart the services Under tools - option -Preferences . So this way you you would not need to schedule the inventory job and inventory would start automatically once you start the backup exec services again .
