How do I connect to asset server within the LAN?

I have been using asset server for many years without issues but today I’m trying to setup my new mac mini running a new installation of Unity 4 to the server (My PC)but I am getting the ‘connection refused, make sure port 10733 is open bla bla’ error.

-My router IS setup to accept connections on 10733.

-My firewall on PC IS setup to accept incoming and outgoing on port 10733.

-I have a setup a host/redirect on No-ip.com which has always worked fine in the past.

-I have tried restarting & even re-installing the asset server .

-Both PC and Mac are running pro copies of Unity 4

-I tried turning OFF the firewall on my server PC and connecting with the MAC but I still got the same error.

-I CAN see port 10733 when I do a port check at canyouseeme.org

Previously I had no issues with my old mac laptop>PC. I am wondering could this be something to do with the fact the machines are on the same LAN? Does anyone know how to get around this?

Rebooted my mac.