My friends and I keep getting this message anytime we try to host an internet game.
We've read "Multiplayer Configuration Readme.mht" -- it was literally no help whatsoever, and the only mention of External IP was the line "your computer must have an external IP address" (no ****!). According to every other way I can figure, my computer *does* have an external IP address. So anyway, I followed every other step in this file -- port forwarding, application support on my router, etc. Nothing works.
I read someone making a suggestion of running Options.exe and putting my IP and Port in the "Public Port" box -- the only problem is that text box is limited to 5 digits, so yeah, impossible.
At this point I've given up. Obviously this game doesn't want to be played and I deeply regret purchasing it.