http://support.veritas.com/docs/276522
If the Backup on Tape was taken using earlier versions of backup-exec, it will ask you to provide a password if you want to password protect the Data on a tape, however from version 11d it gives you the ability to encrypt data with encryption keys. When you encrypt the data on a tape, you protect it from unauthorized access.
If you want to catalog a tape that was backed up using earlier versions of backup-exec, then at the type of catalog operation you will see a PASSWORD field you will need to enter the same passoword so that a successfull catalog operation cannot be performed.
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Sandeep vaishnavi.
Symantec Support.