Please Help Nav Incorrect Position

[bns99121]

I just bought a 2006 z4 3.0si with the MKIV nav system software version 4-1/70 using the 2006 map DVD. The navigation position is changing but it is usually 50 to 100 miles off from my current position. I took it to my local BMW dealer and they said that the Nav system was fine and that I just needed to buy the 2009 map DVD. I don't mind buying it if it will work but it seems that the DVD is not the problem. Why would the DVD cause this? Next chance I get I will check the GPS Almanac, GPS PDOP value, Signal Strength, and Wheel pulses. Any ideas and any help will be greatly appreciated. By the the car is still under warranty.
Thank You,
Neil