I just had this problem about 4 days ago - but mine defaulted to brooklyn. I was driving in VA and all of sudden my map was in brooklyn. I tried everything but couldn't get it to start working properly again. Everything seemed alright - good ant strength.
A couple of days ago I drove by the same spot where I initially had the problem and all of sudden the navigation was working again. I just assumed it was a problem with pioneers satellites (or their licenses to use them), but I guess it wasn't a national occurence.