Excellent post... I have an 06' 750Li with the same exact problem. I assumed it was a loose cable somewhere as it works on and off again. More annoying than an actual problem but its frustrating when you need a working NAV. Was going to save up to have dealer fix this but it sounds like I can save a boat load of money if I clean the ribbon connections myself. Are there any E65/E66 owners that have fixed this issue?
2006 BMW 750Li - Black on Black
2001 BMW X5 - Black on Black
1997 BMW 328iC - Black on Tan