Was there an update to MapPoint in the 18.104.22.168/22.214.171.124 update? I was using the official version (from the CD) and the streets in my neighborhood showed up on the navigation screen. Since updating to 126.96.36.199 when I enter the navigation screen from my driveway I see the image of my neighborhood streets then the screen is redrawn with a generic camera with a line through it (no cameras allowed?) I assume this means that MapPoint doesn't have a map for my neighborhood. As I drive with the navigation screen displayed I do get to an area where the map is properly displayed. I live in a new neighborhood so it wouldn't be surprising that there are no maps available except that they displayed in the original version!
I have tried different zoom levels and I can see the proper map display for a moment and they be redrawn by the no cameras icon (I haven't tried ALL zoom levels.) I have even seen the Microsoft Earth satellite map temporarily and then it is erased as well.
I do have MapPoint 2006 still installed on the system in case that makes a difference.
You have the virtual earth overlay on which is covering up the maps. Just press the virtual earth button to show only the underlying mappoint maps.