Hi,
The fact that the PC can't open the COM-port has absolutely nothing to do with the code in PIC.

The problem is with the USB dongle, its drivers, the USB port or the PC. Plug the dongle into your USB-port, open the device manager and check which COM-port number Windows has assigned to the dongle. Then make sure you select that COM-port in the Serial Communicator.

Another possible cause for not being able to open the port is that it's already opened, perhaps by another program or possibly that some program didn't close it properly. Try restarting the computer.

/Henrik.