This is usually indicating a SCSI problem between the controller card, and the DLT drive.
Some Controller cards are not compatible with DVDSP and a DLT drive, but good results have been reported using the simple Adaptec 2906 Card, and similar good results can be had with the Adaptec 2940U2B. You will need an adapter cable to convert from the SCSI-2 format (68 pin) to the SCSI-1 format (50 pin Centronics connector).
Don't forget proper SCSI termination, which can also prevent proper operation.
