About media that is missing in robot
Duplication may fail if NetBackup does not know that a requested piece of media is in the robot. For example, a tape may have been moved to the off-site volume group inadvertently even though it remains in the robot. To compare the tapes actually stored in the robot with the Media Manager database, use the NetBackup Administration Console Inventory Robot option.
If the tape is not found, delete it from the NetBackup system. If the tape is missing yet is assigned and has valid duplicate images, use the command bpexpdate to expire the images before you delete the tape from Media Manager. This command is documented in the NetBackup Administrator's Guide.