Oh,man,I hate bluetooth!But trying to help,in sympathy, firstoff,XP has trouble "telling" an app what the ports
available are above a certain number(is it 10?) while bluetooth drivers love to go crazy into the 20's.
One fix that seems really easy for me is XPORT which'll connect em together by finding the Bluetooth port and allowing you to reassign it a lower Port that XP will allow to OpenCPN.
A harder fix is in Device manager....where all the doofunnies and their ports
can be seen.You CAN reassign the port a lower number by tunneling into all the options(properties,advanced...you know)but you may have to reassign something else first to make it free.And of course you need know which of the many ports bluetooth is using is the nmea one.-Usually,it's a serial
port?By the way,the bluetooth need be plugged in before doing this but I belabour the obvious,because that's what I
Maybe,too,while you are in there,on the "Properties"page see if the thing is communicating at BitsPerSecond 4800.It might help it might not.
I have too many other ideas but these are the first that pop up.