there is a way to re-calibrate your position...
p. 42 of this nav. manual
http://www.bmwmotorsports.org/pdf/BM...20-%202004.pdf
park in front of a known address. better on a residential street. or do it at the intersection of 2 streets the nav easily recognizes. make sure you are parked facing the proper side of the street, meaning make sure that the address you will be entering is on the right(not left) side of your vehicle. then, enter the intersection or address in the system as directed.
i did this when i had to get a new nav unit and it's worked pretty well.