Reading PC CD-R's on a Mac

Doe anyone know of a way that I can use data stored on a CD-R on my Mac. I have tried several different methods, and they all treat the disk like it is completely useless.

I have tried to mount it in a Mac CD-R using toast, tried to rescue files from it based on pattern searches with Norton, tried to "repair" it with Norton. I've tried just about everything I can get my hands on, but to no avail. However, when I throw it in my friend's PC CD, no problems.

Explanations, comments, ideas? I'd love to hear them.

WHAT OS ARE YOU RUNNING WHAT MODEL ETC.