Well this is an error that I get from time to time, but it's not an error I can offer good advice on without seeing it myself.  It's never been a recurring error with me, and isnt something that happens every time I play, for me it usually happens when I am surfing the web as well as playing minecraft on World of Minecraft and the change between the windows locks it up.  It's the same type of error that I get on firefox, or any other program that just needs to be restarted (because it locks up), but if this is something that happens every time you play it is quite strange.  My suggestion, first try redownloading World of Minecraft, make sure its 2.0.6.  Try logging in with the valid box unchecked to the server that you want (or World of Minecraft realms if you want to attempt a login on one that is almost definitely up).  If that doesnt help, I'd say that you may need to update Java, so try that.  Hope this helps you, but like I said, its strange to get something like this as a recurring error, and it might be a problem with your computer itself.