Got kicked out of the game 10 minutes ago, reason "new update available, can't play blah blah etc..."
Ok, fine, no problem. Close the client (standalone, PLEASE acknowledge there are people who don't want to use Steam out there)
Everything goes fine, no update.
Start suspecting something's wrong
Message "client out of date"
Repeat above steps two times
Deleted client executable, launched updater once again. This time it went through the full update, but game still can't start. Also, the "new" client executable is identical to the previous one.
Verdict: it looks like it's not some obscure bug or configuration problem, you just forgot to upload the new standalone version of the client to your server.