TT5.1 - 'no valid signal'

I've looked through the sticky's and relevamt threads but have got confused!

Am using TT5.1 on an iPAQ 4150 sitting in a Holux car craddle kit etc.

The holux diagnostic tool finds the gps reciever and it gets a lock. 4800 baud on com1

TT5.1 doesn't. the little yellow disc spins away and the UTC is picked up, the circle map seems to indicate the position of some satellites but the message remains 'no valid gps signal'. select any other baud and i get the 'no gps' message, so I guess I'm close!

I seem to have read that TT3 fixes something????? I haven't got TT3 I'm afraid.
anyone any ideas/suggestions?

many many thanks in advance