Uncheck secure connection while creating your comport.
Another to remember, A device that does not allow you to change its pairing code technically doesnt have one. Is just like having a blank code. Most bluetooth devices, like headsets etc, use 0000. Not too hard to crack that one.
However, I am not sure if the bluetooth devices use that code every time the device connects. So if you connect and use something other than 0000, it might not work the next time you turn the GPS on. I would recommend doing what it takes to use the 0000 code.