Well, Saturday and getting the same problem. My friend here logs in successfully, but my machine appears not to do so fully. Symptoms as follows:
After clicking 'ok' in the Lobby Login dialog (Name pwd serial already populated correctly), I get 'connecting the Lobby System', then ' Gateway to Caen Multiplayer Lobby', click 'ok', and now I can see members in the lobby users section, but already I get a dialog titled 'Close Combat Error', reading 'Get forum root failed. Unknown error.' and a box 'ok' to click. I click 'ok'.
Now I can receive chat messages, but it is very noticeable that the Matchmaking Forum window is failing to populate. When I click 'join' it says 'connecting to opponent', and then I get 'Close Combat Error' 'Connect to opponent failed. Unknown error'. I click 'OK'.
The dialog titled 'Close Combat Error', reading 'Get forum root failed. Unknown error.' reappears and a box 'ok' to click. I click 'ok'.
When I try hosting or connecting to Barnaby (who is in the same room in the same house with me we get as far as seeing the message saying that he is asking me to join him (or vice versa), but when the other one of us accepts, we both get stuck in a 'connecting to opponent' dialog without it ever connecting.
It seems to me that this may have something to do with the fact that the forum fails to populate. Presumably some part of the connection is getting blocked? Yet I've looked into my router settings and it doesn't appear to be blocking any ports. I can't see why it wouldn't be working.
Any suggestions gratefully received. It is a recent download (since the New Year 2016) direct from Matrix games. So I presume it should be the latest version.