-- Restart all BEWS services and then try to perform a restore operation.
-- If this does not help, then perform following steps :
1. Open Backup Exec
2. Go to Devices tab > Right click on the tape drive > uncheck "Enabled"
3. Again right click on the tape drive and select "Delete"
4. Stop all Backup Exec services
5. Start all Backup Exec services, and verify if the tape device is detected.
Now, try to perform restore job and observe the result.