burning / reading

Hi,

My MacBook ('07, running Snow Lepoard) won't read copies of my legitimately ripped and burned (I own the discs and copy in case of damage or the failure of a friend to return the original I loan). It doesn't matter what drive I use (internal or external). I never had a problem before Leopard came along.

I use "MacTheRipper" to rip the discs. Frequently it won't "see" the disc or report an error

At this point, neither will the Mac read the discs that used to work, attempts to burn invariably fail. What gives? How do I fix it?

Thanks for your time,

Dave