HP ultrium tape drive problem

Hi
i have installed a HP ultrium 960 to a Adaptec 29320A-R on HP proliant DL 380 G5 server,the tape drive is connected with a external scsi cable and scsi bus is terminated,server’s os is Windows server 2003 R2.
the problem is when i try to get a backup in ntbackup it say that you should make free the media and when i free the media in computer management/removable storage it shows that is in “wait for writing label free”mode,but it doesn’t finish it .
i can see 2 error in Event Viewer after that:
Event Id:11
Event Source:a320raid
———————
Event Id:1003
Event source: SytemError

can eny one help me?