SQL Server 2000 tape back-up

we have sql server 2000 running on Win NT 4 server. The system has a DDS3 tape drive for back-ups. The OS can find and write to the tape drive. Problem is when trying to get SQL to back up the database to tape it reports that “//./tape0 is an unknown format” the drive is selected (obviously) in SQL as the back-up device but can’t write to it. Any ideas??