CD-Rs, especially cheap, crapy ones made by Ritek or CMC Magnetics, or even worse companies like K-hypermedia, have a nasty habit of going bad, sometimes even if you properly store them in a cool, dark place.
The best suggestion I can give you, is to try
IsoBuster. It has recovery and multi-format reading abilities that may help you get back most or all of the contents of that, or other discs you have that are going bad.
I'd suggest having a careful look at any other CDs of the same or similar brand and age you have lying around, you may want to get your data off any that are giving you trouble, and burn them to new discs after recovery.
My Eyes Are The Victim's Eyes.
My Hands Are The Assailant's Hands.