why is my volvo RTI system showing the wrong location?

RTI system is showing the wrong location. Have tried re-loading the disc, leaving the system on for 30 mins while driving around (in the hope that it would update), displaying 'current location' info several times.
System seems to be working as normal apart from wrong location - I'm in Maidenhead but it shows up as being in Southampton! In case it's relevant - it is showing no. of satellites as 0.