iPAQ 5550 problems

Hi,
I'm having problems with my iPAQ 5550 running Winpilot Pro, wherein the
screen freezes at various times in flight, requiring a soft reset to get it
working again. It's driven from a Colibri and Borgelt B50.
It occurs especially when a task has been set and the start button is
pressed, but it also happens at various times during the flight, and it
happens again when trying to Quit Winpilot. Needless to say, it loses all
flight info and trying to reset the thing in a comp with 60 other gliders
milling around the start is not a healthy situation.
I have tried a hard reset (on the ground of course), I have disabled the
airport file, I have deleted all previous IGC flight files, I have disabled
the terrain function, I run no other programs on the thing, Bluetooth is
disabled and Infra red is disabled.
Not to mention the fact that this is the second 5550 that I have had that
does the same thing. I took the first one back when it did it and the shop
gave me another one. Previous to that, I had a 5450 that ran well till I
dropped it and bent the connection pins, so to me it seems like there is
some hardware compatibility problem somewhere with the 5550.
Is the 5550 a dud and should I just chuck it out the window and get a
different model iPAQ (one that works), or is there something else I can try?
Thanks.
Phil