So a couple weeks ago my GM Factory NAV DVD became no longer readable by my stock NAV head unit. I think the surface of the DVD got scratched when putting it in or ejecting it. I read on some forums you can burn a copy by using decrypt to extract an iso image of the disc and then using a program like iclone to burn it to a DVD. I did that, after polishing the surface of the DVD enough so that my computer could read the disc. Before i bought some double layer DVDs, I burned a few single layer DVDs by removing some of the files out of the iso until i was down to under the capacity of the single layer DVDs. The size of the iso file went from 5.5 gigs to about 4.3 gigs. Well, the only DVD that works repeatedly with the unit is one of these canabilized single layer DVDs, even after burning 8 or so double layer ones. The radio reads it like a champ and i am back to having a functional NAV unit but LOL i think because of files i removed it now thinks that i am in a city in Michigan.. and thinks my home is over 700 miles away when i put it in as a destination. Is there a factory NAV guru that knows how to burn a functional DVD and/or why this single layer DVD works so well but the unit thinks i am in Michigan?