Right, well basically I started playing The Frozen Throne again with a mate, and due to us both having routers, it's hella annoying trying to both get into a game, let alone a game we both wanna play.
So I found out I could go over to PortFoward.com, sorted out that stuff out, and got all the way down to enter my IP address as a URL, and logged in, bla bla bla. Then I got to this screen:



I've filled it all in, as PF tells me to, but then when I click Apply, it just says 'Invalid IP address'

What do I do? PF says to leave it blank, and I've even tried it as 0.0.0.0. I've also tried using my own IP address but still didn't succeed. All help appreciated.