For all those who are having the steam authenticating problem, I have found a solution!
Right now i am playing spiral knights and i had this error before, i simple went to Library, then right click on spiral knights, then open your properties, after that go to local files and then click on Verify file intergrity, now a downloading will happen in which everything will be fixed and you will be hunting those black kats in no time
For all those on Steam having authenticating problem
Mar, 05/06/2014 - 21:42
You don't need to do that. It works now.