Navigation showing incorrect location

It's really hard to say, but one thing that occurs to me is that your map database might have an error. Have you ever updated to a more recent DB?

 

Try the nav manual. My other car's nav has a calibration procedure.

If it's only off on a very few streets, then it's probably the map info and you can;t fix it short of buying a new map DVD, if it's off most places, then a calibration might fix it.