Steam Firewall preventing playing Rebellion

I have played Rebellion previously on Steam just fine (when they had the Advent update)... But now I can't play with the new update (with the Vasari). I get on Steam, and it doesn't even allow me to update the game to the new update. In addition, every time I click play, it comes up with "Performing first time setup... Installing Firewall 1 of 1" then exits out of that window to another: "The game is currently unavailable. Please try again later." The last time that it would work, which was before the Vasari update, I had Avast! on and it never conflicted with me playing the game. I turned off Avast! now, wondering if that may help. It does not, and the same two windows pop up after clicking the "play" button on Steam.

I understand that the full release is just a few days away... but I've had this issue for close to two weeks now, and I've tried to look up potential solutions... but I'm not tech-savvy enough to know exactly what it is I'm looking for or what I need to do to fix it. If a solution to this problem has already been listed, please send the link.