Note that if you update the game then firewall will often block the changed EXE, you may need to reauthorise (assuming that the problem is firewall related of course).
Cheers
Pip
Lukas -> RE: Multiplayer (5/28/2015 2:33:20 PM)
Personally I have to run the game in windowed mode to get my firewall "allow connection?" popup to show up (ESET Smart Security). After checking the "always allow for this application" I can connect in full screen as well of course.
So if you are used to getting a firewall permission popup and you don't get one here, try windowed mode first.