How come itunes is saying my "disk is full?"?

I'm trying to add a couple of CD's into my itunes library, but a little box keeps popping up saying: "The disk you are attempting to use is full. Removing files and emptying the recycle bin will free up additional space." First of all, it's a little weird because I only have 500 songs in my library right now. But I emptied my recycle bin, and deleted several songs, but it's still not working. I managed to add several CDs before this happened. What could the problem be?