Cdr Can't Be Read


I have a 1gig 17inch iMac running OSX 10.2.8. I have a moderate understanding of tech.

The burn process runs OK in iPhoto (4.0.3 ) but when I put it in the mac to check the burn, this msg. appears...."You have inserted a disc containing no volumes that OSX can read." I have tried several brands of CD with the same results. In the past I have burned many discs with no problem. How can I back-up my library now?

thaiks, Bill