Tom Tom 5 with "Socket" wireless GPS

Hi
Running TomTom5 – was on Navigator 3, iPAQ 2210
Changed to a “Socket” wireless GPS which worked fine with Tom Tom 3 but cannot get it to work with TT5 – very poor signal
I reverted to the hard wired receiver - worked fine - good signal on GPS Status and showing 5 bars on navigator screen.
Changed to "socket" GPS and reconfigured TomTom.
After about 30 secs the GPS Status showed 5 bars - in grey.
After further minute they changed to blue so switched to navigator screen - only showing 1 bar on screen but showed current position. Set off for destination and system worked (with only 1 bar on screen) for about 1/4 mile then "No gps signal".

Stopped and checked GPS Status- still showing 4 bars in blue and connection status OK. Continued but never received any on screen guidance and still showing "no gps signal".

I have a magnet on the GPS receiver to fix to dash - thought this might interfere so removed - still no signal getting through.

As TT works perfectly with hard wired receiver and did get brief communication from "Socket" I can not decide whether problem is with “Socket GPS” or TT5 software – any ideas ?