Sony 6 CD head unit - CDs stuck!

[Zippy7]

Was driving home today, and my daughter asks to change cd to disc 2.
This worked fine, then next traffic lights, I notice the head unit shows a "No CD" error. But it's playing perfectly fine... Very strange.
When I get home, I try ejecting, but no luck. Seems very odd that it can play the cd that is in there, but doesn't recognise there are 4 cds loaded in there.

Anyone have any suggestions? I've turned the stereo on and off a few times, and held down the eject button, but no joy. Was not going to do too much as I figure this should be a warranty job for Ford if there is no simple fix.

Cheers.