When I try to forward my ports for netplay, I keep getting this error when I put my "IPv4 Default Gateway" (As said in Connection Details) in the private IP area:

I'm running Windows 7 Home Premium and my Router is a Belkin Play Max N600 HD (F7D4401v1). I've tried PortForward's tutorial and I've tried the help sticky, they don't work. Can anyone help me?