Slot-loading drives can be picky about discs, even if they aren't visibly damaged. I'd say about 2% of my discs wouldn't work when I ripped my CD collection.
I used an older iBook with a tray loading drive and it worked fine. Might have to track down another computer and give that a try. If it happens on a lot of discs, you might want to check with Apple to see if perhaps the drive is defective.