I updated Spiral Knights today (judging from the forums it was the update to revert the danger missions), and since then I'm unable to log in.
I play through Steam, and when opening SK it'll send me immediately to the knight selection screen (as normal).
When I select my knight, it attempts to send me to the ready room but instead sends me back to the log-in screen with the error "you have been disconnected from the server."
If I press "Logon" again, it'll attempt to log in indefinitely. It doesn't freeze, as everything is responsive; it just won't log in.