I had the same problem and it went away after I played the tutorial. That's the only explanation I can offer. Maybe give it a shot if you haven't
Alright so after I came home from work I started it up, played the tutorial, and then was able to play flawlessly. So, not sure if they fixed something or if you HAVE to complete the tutorial, but it works.
It happens every match
NA server. Haven't tried again since last night. Will try again when I get home from work.
So, I just freshly re-installed the game and it starts up fine, I can go through all the menus and my inventory, but when Im asked to pick a class at the beginning of a match, I get returned to the lobby due to an "unknown error". Not sure what it could be but there it is, thanks!
PS the game ran fine during CBT if it means anything.