If this is happening during duplicates jobs running, this would be due to an error occurs during the relocation of DSSU images to the final storage unit, the operation must be retried manually. For example, if a Status 134 is encountered during the relocation of images to tape, the duplication job will fail with a Status 191. If a duplication fails with any error code, the parent "
__DSSU_POLICY" relocation job always returns a Status 0 (successful) in NetBackup 5.x. Since the parent job receives a Status 0, and not a Status 134, the job is never retried. Duplications from a tape or disk storage unit also need to be retried manually if an error is encountered.
Take a look at the Netbackup technote.
http://support.veritas.com/docs/279718
Can you provide a bit more information as to when you see this error to be better able to tell whats causing it.