(POSTED FOR FUTURE READERS)

I had a similar problem with my MKIII. My Navigation screen would go black, periodically reboot, and my Navteq navigation CD would constantly eject itself even though it was flawless.

I would recommend trying to DOWNgrade your Nav software (to v21.1 which brings you to 3-1/62) and see if that fixes the problem. If it does, you can always use any of the later versions of the Nav software to bring you up to version 3-1/63). It worked for me.

Good luck!