Informix tape tar error on IBM RS/6000

I wanted to reconstruct files system in IBM RS/6000 model 380. The OS is AIX 3.2.5. The load line of Informix tape is "tar xvf /dev/rmt0". When I tar the Informix tapes, always got a message "tar: 0511-169 A directory checksum error on media; 0 not equal to 13699.". There are 6 tapes got the same error on Ver AH5.04.UC1 products. I checked the tape device setting. The Block size is 0. It's mean variable length. And I tried "tar xvf /dev/rmt0 -b 0". The Block size from 0 to 20. No one block size can work. I tried "cpio -icd < /dev/rmt0". It cannot work too. Everyday I made a Achive tape, it is normal. I tar own file system, it is normal too. Last month,I return all tapes to the Informix agent. And I got new tapes in this month. But the error still happen. What should I do? Try another command? Or return the tapes again. -- Madeline Wu from Taiwan...........