My understanding is that ports below 1024 are system ports related to the operating system and so you should keep away from them in case you select one for something that will later try and run and then fail because the port is already used.
I suspect that in the cgi perl code for the n2n connection it checks if the selected port is a system port and prevents you using it and I would expect that the same is expected for the rw connection but the software check has not been included in the code.