Running SBS 4.5 with Veritas 7.3 rev 2370

What usually happens on a regular basis a scheduled backup will fail with a
CRC error or bad sector on tape. I will manually schedule a job
for 10 minutes later and backup will execute successfully.

I have applied all the suggestions from tech support
disable synchronous and Wide negotiating, 5MB tranfer rate, latest veritas
drivers on all my servers.

I also retention tapes and perform quick erases.

What else should I be doing.

Doesn't make sense that I have to continually perform retentions and manual

Any Help appreciated