Friend of mine bought a new 2007 Escalade (loaded), took it on a trip, said after 3-1/2 hours of driving the Nav locked up on him saying "Disc misread" or something like that. Still didnt work after turning car off, then back on. Only worked after the car had sit a while, then it would work.

Is this a know problem with 2007 models or a problem with other model years?

I've used the nav once in my EXT, and had no problems, but it was only an hour plus drive. I've never heard any problems with it. He should just have the dealer look at it. You either have the DVD Disc that's bad, or the DVD reading element, or not getting the GPS to pick up where the car is located. Either way, take it to the dealership.