NetBackup will freeze or suspend media if it meets certain conditions (a specified number of mount/write errors, etc.).
If you would like to unfreeze a tape, you can use the bpmedia command below:
/usr/openv/netbackup/bin/admincmd/bpmedia -unfreeze -ev
To unsuspend a tape, you can use the bpmedia command below:
/usr/openv/netbackup/bin/admincmd/bpmedia -unsuspend -ev