The matchmaking server is currently taking a little more load than it's used to, so room creation may be a little difficult.
I'll be implementing Steam matchmaking to ensure every room gets created without a problem today and tomorrow.
Steam Invites appear to work only when the game is not open. This will be fixed in tomorrow's update.
The OpenPort tool might be being blocked, so if it says server unreachable, please open it manually and it should be good.
Also, some achievements are currently unreachable, this will be fixed in tomorrows update too.
Hope you enjoy the rest of the game without bugs, anything unusual please report in the discussion forums and I'll immeadiately start working on it!
Thank you.