I think we've already pointed out what the problem is:
Nero 9 is a buggy and bloated program, which no one I know likes.
You're not using reliable DL media.
What else do you want us to tell you? Stop using Nero and stop using crappy media.
We don't care what media is on the supported list or what software is popular in the marketplace, you came here asking for our expert opinions. We gave them to you. Now, it's your job to act.
I'm not trying to be mean, but when you're using software and media that we wouldn't use in 1000 years, what can you expect us to tell you?
BTW, I assume you bought those Optiarc drives new, because if you didn't, then you're really on your own. And make sure the firmware on each of them is the same and up to date.
And one other thing, this should be obvious, but make sure that every single program you are using is up to date. Go to the Nero and Alcohol web sites, and download any patches or updates.
This might also help: