I get this here and there... but is MP3 cds... which I record myself cause for some reason my MP3s sound better and louder than in my Zune... but anyway this happens when I try to make the unit read the folders and kind of freezes and even acts as if theres no cd in the unit. So what I came up with to take the cd out was just to park the car and turn it on and off until the unit detects the cd, (you know, when you can finally hit the cd tab) and eject it and dont even dare to insert the cd again... :-\
I kinda breezed over this just this past weekend reading the owner's manual. It says if a CD ever gets stuck and won't eject, hold the eject button down for about 5 seconds and it should come out. Hope this helps. Now why it does it, I have no idea...maybe a trip to the dealership can help.
I had this exact problem last week while experimenting with an MP3 CD. Holding the eject button only popped open my NAV screen. I finally got it out by turning the car on, then off, opening the driver door, and then hitting the eject button.