copying cds to desktop folders

Hi can anyone tell me why, after having spent a couple of days copying cds to folders on my Mac, now with no warning or changes to anything that I am aware of, suddenly when I drag files from a cd to a folder, I get a little no-entry sign, the files are greyed out and they will not copy?

Is your hard drive full?

Hi, no I've only used about a third of the memory, so no issue there. Is there any limitation (from the Mac's point of view) on how much you can download. Is there some kind of downloading memory (Not Hardrive space) perhaps in the operating system memory that has a limit before it needs to be reset?

Are these commercial CDs you are copying? Some manufacturers use blocking devices to prevent duplication.