In addition to earlier post,
You need to Stop and Start the Backup Exec Services. (From CONTROL PANEL | ADMINISTRATIVE TOOLS | SERVICES)
Please refer to the following technote's :
http://seer.support.veritas.com/docs/254826.htm
http://seer.support.veritas.com/docs/191188.htm
If the Backup Exec services are killed then the tape device will need to be re-enabled in Backup Exec for another backup job to proceed.
However if you still want to kill the services, please refer the following technote's for the same:
http://seer.support.veritas.com/docs/230521.htm
Hope this helps.