Barney,
Give us a bit more information about your system.
What Antivirus do you use?
What firewalls do you use normally?
Be sure to recheck that you have all the numbers typed in correctly on your router rules, end port is same as start port, internal ip is listed and not your gateway ip. Make sure the rules are enabled if needed and that you have the protocol set correctly.
Then verify that your WinMX is set to also Listen on that TCP port, and Send and recieve on that UDP port listed on WinMX settings > incoming TCP and IN/OUT UDP