Honestly...I hope for you (Rick) that it solved your problem for good.
My 2 cents? It's rather strange that all of a sudden several users complain about this specific error with each it's own different hardware...
I use Veritas Backup v10 in an upgraded computer (working as file-server), it worked for almost one year without any problem, and then all of a sudden the error occured. After some searching I found this thread with exactly the same problem for several users...
I tried almost everything (changed drivers, reinstalled card, reconfigured Backup Exec, ...), I'm willing to reinstall Backup Exec, but I'm not going to reinstall my server as I am almost convinced (yes, sometimes I can be really stubburn...) that it is due to the software. Unfortunately it is impossible to test the hardware somewhere else, because the file-server has to be 24 hours, 7 by 7 up and running.
Same problem, little amounts of data -> no problem at all. Once above an half an hour of backing up, it gives me the error...
The SP4 as mentioned before did not solve my problem either...
So, I'm still waiting for a solution of Veritas (Symantec), because, again just my 2 cents, this problem is due to a problem/conflict/... within Backup Exec.