I've added a CD's worth full of MP3 tunes into the multichanger with some ordinary music CD's and the one with the MP3 tunes on it comes up with error but obviously the unit has no problem playing the others. The mp3 CD plays OK on my pc. Ideas ?

The usual cause is the way the disk has been burnt, or the software used. Disks created with iTunes for example dont work. Use Nero and burn as a data disk should work fine. Just make sure they really are MP3s and not iTunes M4A (AAC) files as the bolero cannot play these AAC format files from CD.

Is the disk finalised?