On Aug 11, I've been able to play, but recently, this afternoon, I was unable to log in myself. I figured it might be a problem with just Kongregate, so I looked at the discussion on the Kong page, and there's been similar problems.
So, recently (I'd like to say around August 11), there's been a lot of discussion in Kongregate's threads about being unable to play Spiral Knights through there. The fix at the start menu says to restart the client page, but after numerous attempts, the errors have not been fixed. Is it an issue with the Spiral Knights and Kongregate information being relayed?
At this time it looks like Kongregate is still struggling to serve content to many players. It appears they are still working on fixing the content delivery problem.