This has happened to me before. I think it was because I burned an ISO9660 CD using Toast 5 with settings that it didn't like. IIRC, I had it set to "allow Macintosh names", and some of the files had names that were greater than 31 characters (the limit in OS 9, but not in OS X).
I'm pretty sure there's no way to get the files to work on OS X. Burn the disc again, taking care to use names and formats that are compatible. Sometimes it's hard to know what's compatible with what, though.
For what it's worth, I've never had the problem with Toast 6. That might just be coincidence, though.