Try this:
" What to do first is slide a credit card under the magazine until you
hit a lever , this lever holds the mag in place and if you press it
hard enough to push the lever it should pop the magazine out.
If this doesnt work youll need to open up your changer, ie remove the
screws and take the outer casing off. At the bottom of the changer is
a large cog, turn it until the CD reader is at the very top then try
the credit card trick above, the mag should pop out this time. "
(cut and paste job from a google thread I bookmarked)