Sounds like they’ve used cheap crappy media, or media that your drive does not like. Try Isobuster, or another recovery program to extract the files to your hard-drive. It would also be worth trying other drives if you know someone else with a pc. Some drives are [I]much[/I] better readers than others! Also make sure your disks are spotless before you put them in the drive.
I’d give Isobuster a try first though. It’s recovered a lot of stuff for me. Just put in the disk, open Isobuster and highlight the files you want, right-click and extract. You can change the options so that it will make more attempts to read the more stubborn files as well if the default settings don’t do it.
There are other free recovery programs if you look around the net, and If you know anyone with a lite-on or asus drive, you may well be in luck there too as they tend to be able to read better than other drives.