Hi,
We suggest you to follow the steps given below,
1.Uninstall the Veritas associated drivers by using the Tapeinst.exe utility.
http://seer.support.veritas.com/docs/199881.htm
Here when "Choosing Tape drivers" screen appears then select the third option of "uninstall and remove all Veritas drivers".
2. Now Go to Devices tab ;Right click on the tape drive (If it is showing) > uncheck "Enabled".
3. Again right click on the tape drive(If it is showing) and select "Delete"
4. Stop all Backup Exec services.
5.Now delete(Uninstall) the Tape device from the Device manager.
6.Reboot the server and verify that Tape device is detected and Microsoft driver is installed.
7.Start all Backup Exec services and verify if the tape device is detected.
8.Now again follow the Technote:199881 and follow the steps to install the Veritas drivers .
We hope this resolves your query.