Are you trying to backup TO the NAS to a B2D folder, or are you trying to backup data FROM the NAS to a tape attached to your media server?
regardless, I'd HIGHLY recommend the free upgrade to v9.1 SP4a
v9.1.4691.1 here
http://seer.support.veritas.com/docs/264658.htm
SP4a here
http://seer.support.veritas.com/docs/280008.htm
HotFix 56 here
http://seer.support.veritas.com/docs/282260.htm
DriverPack here
http://seer.support.veritas.com/docs/273853.htm