When trying to join a private game without knowing the password, I got a wrong password message, then a Processing Request window which stayed there without activity afterward. I needed to refresh the page (thus logging out and back) to be able to access the lobby again.
Thanks so much, Jaels- we'll have a fix for that in the next update.
Something along the same lines happened to me after trying to join a still "open" two player game that already had 2 players. Game asked me if I wanted to be a player or a spectator, I chose player to see what would happen, and got the "Processing Request" message for ever and ever. This sounds like the same issue as Jael's