Have you tried reburning any of the discs that are giving you problems? If you're sure that the problem games should work, and you do get some games to work then I would say that you are having problems burning discs or some discs are faulty out of the package.
this is how I burn discs
1. burn at 4x
2. verify the burn, to assure the disc is good and the burn matches the ISO
3. no multi tasking while burning, no touching the mouse while burning
4. make sure the screen saver or virus scanner no start running while burning