Excellent explanation on the many problems the legacy COM ports can bring. There are however a couple of things that must be mentioned to make the list complete:
1. If using Vista make sure that you have Administrator privileges. And, no, it is not enough to be logged in as an administrator because of the new UAC or User Account Control in vista. I had problems in my laptop not allowing traffic from the Bluetooth receiver. I had to turn off the UAC in order to get the thing to work. To do that, in the start menu select control panel, there user accounts, and then turn User Account Control on or off.
2. This might sound like trivia, but sometimes it happens, two applications cannot access the same port simultaneously. Make sure that no other software is accessing your port while trying to read from it.
In GAS there's support up to port number 144, so it shouldn't be a problem if you have a high port number on your device. Well, below 144
We are trying to implement the genuine USB GPS, that is without virtual com ports, but except for a few models from Garmin it is very hard to find documentation for the drivers.