I've got a 2000 S4 2.7 twin turbo with the genuine sat-nav and tv fitted. Driving along either on show map or directions, the unit will, after a while, re-set itself as if its just been switched on. Worse still, when it comes back, sometimes there's no roads on the map, just a blank white screen. (Maybe I've being whisked away by aliens?).

This is driving me mad as its got to the point where I can't rely on the sat nav for directions!!!

Strangely enough, it seems to do it when I go into London but sort itself out when I get back towards West Sussex. Could it be data overload?
I have considered following the instructions on here and re-loading the software but am reluctant to do this unless I have to as I am not that genned up on it and don't want to do further damage or render the system completely useless..
Can anyone help???
Thanks in advance,
Robscim