itunes allows you to download music off the internet. When you do this, you are only allowed to use that downloaded song to create a set number of CD's. They end in the file format m4a. They are protected, and thus you can't use it! Im not sure if this is the case, but do a "apple I" to get the info. on the CD. If the "Kind" is MPEG-4" then its protected. Also while your there, check the Ownership & Permissions. It should say you can "Read & Write".
Hope this helps.