Final error: 0xe00084ed - A hardware error occurred.

I am running Windows Server 2003, BE 10 Rev 5520, with all updated firmware & drivers using HP Ultrium 960 autoloader with HP Ultrium 3 new tapes.  Backups and restores were working fine up until a few months ago.  At that time I started getting the above message and then the autoloader goes offline - usually during a full backup after it had been running for 3-5 hours.   After the server & tape drive is restarted, backups would run again for a few days, then I'd get the error again.

I worked with HP support who found nothing wrong with the drive; I changed out cables, terminators, and then a new U320 SCSI adapter (recommended by HP for their drive).  But, still having this problem - it works on small backups under 10GB, but have the hardware error on backups that run longer than few hours.  Backing up to disk works fine, but I've only tried relatively small backups since I don't have enough disk space for a large one. 

Any suggestions would be greatly appreciated.