Hello,
I have same problem. Just can't understand why now it's year 2017 and didn't fixed that or updated since 2013.
I work as a developer, I would really love to see solution how to fix it, or be able to fix that, but there's nothing even on the internet.
My exact problem is:
I am on WIFI, create new public game and waits in lobby.
My girlfriend have notebook next to me and is also on WIFI.
Game shows in Available Games, but when clicking to Proceed, it just starts loading and nothing more happens. It never stops.
(I have Win10, she Win7, no errors displayed, error log not found, even forwarding on WIFI is set to one or both of laptops)
Tried also by invitation from Steam, but that was less lucky.
I bought two of this games at once, to be able to play together, so I am pissed. I havent noticed that the game on sale is already abadoned without further support?? That was reason for sale, for such a low price. Wasn't?
But to the point. Does anybody really knows how to make multiplayer working?
Without multiplayer working, I will hope for refund.