Unity Networking - How to determine if NetworkServer is not listening on port.

I know this issue can sometimes crop up especially when testing on the same network:

Cannot open socket on ip {*} and port {47775}; check please your network, most probably port has been already occupied

But when you run the function it ALWAYS returns true. I basically want to make an error message on screen if this error happens but I can't determine a way of doing it.

Any suggestions?

Thanks,