out of date server

I’ve recently started working with a company running NT server V4.0 SP5 and Exchange V5.5. Seperate server running Proxy 2.0. My question is regarding the Seagate 12/24 DAT installed in main server. Server has two SCSI cards, one Adaptec and one no-name. There are 3 SCSI hard drives in server and all hard drives and DAT drive run off the no-name SCSI card and the CDRW runs off the Adaptec card. We have over and over again had tape backup failures saying “bad media”, replaced drive and cleaned, to no avail. Do you think the sharing of the SCSI card with Hard drives could be the problem? Thanks.