I'm not sure when this issue started popping up for me, but I've seen I'm not alone.
It started with my using the 'logging via steam' button and immediately getting disconnected.
I followed the 'clear password' solution and entered my current password for this very account as per instructions... However no dice. I'm getting Error: Invalid Password when I try.
Thus far the following things have not worked:
* Changing password and using that
* Manually entering my account name and password
* Validating the game files on Steam (multiple times)
* Running Steam as admin
* Restarting Steam between attempts
* Clearing the Steam download cache and signing into Steam again
All of the above results in the same Error: Invalid Password (or Username or password is incorrect when I do it manually) and I can't really think of anything else to do and there doesn't seem to be anyone else that hasn't had their error solved by the above steps in some way.
Additionally, when I play ranked (or rather, attempt to) the countdown freezes at 0 and I have to restart the game to try again, which is rather bothersome, I've never disconnected elsewise in the game and the countdowns when I actually get into a game work perfectly.
As for the 'fix' to reinstall Adobe AIR, that's not really workable as it's not installed to begin with, nor am I running my computer on WiFi, it's on a wired connection.