I am making music CDs and I should be trying to make data CDs?

That might be the problem. And don't feel like an idiot, it's not something they make very clear.

I mean, someone who doesn't already know about the technology, if they want to make a CD full of MP3s, might assume "MP3s are music, so I pick music."

Even some of the replies by the people in this thread who know the difference, made the assumption that if you wanted to burn a CD of your MP3s, that you really did mean an audio CD.

Anyway, to give you the background, CDs are made up of either audio tracks (like the music CDs you buy in the music store) or data tracks (like the software CDs you buy at the software store).

Whick kind you burn depends on what you want to do with the CD. If you want to store computer files like MP3s, like Paul said, then you make a data CD and drop the files onto it. If you want to play it in a stereo that can't play MP3 data CDs, then you need to make an audio CD.

Look at the bright side. All those things you think are coasters are probably playable on your audio CD player.