If it's a DVD-R/+R badkup, it could be a flaky burn. Double check your media against your drive's firmware. (There's a sticky about test utilities up top). If your media passes for 2X and you burned at 1X or 4X, try it at 2X--this usually solves this type of problem most of the time.
Otherwise, it could be your 3.1 chip. I don't have a magic, and I'm running a v5--but I have seen posts about issues with a v7 and a 3.1 magic. I just broke down and bought FF-X2 to give my l'il v5 a -R break for a while--I'll trade it for Xenosaga2 when it comes out in a few months (hope it stays on schedule )
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.