Patrick, I looked at those already, but thank you anyway. I think advice #1 might be the best in this case, sadly...
I haven't burned the playlist more than 10 times so I know that is not the problem (and it's an actual burning error, not a message saying I'm prevented from burning), but I was wondering about that statement, because it says in the iTunes marketing material that you can burn as many CDs as you like.
Does it mean that I would have to rename the playlist, in the unlikely case I'd want to burn more than 10 copies? Or does it keep track of the song collection itself?
I got a plug-in for Nero that lets it burn MPEG-4/AAC files to an Audio CD, I'm going to try that a little later. I'm assuming it won't work though, since Apple has DRM on the songs from iTMS.