I've done a bit of searching around various forums and couldn't find a decisive fix for this problem. I've owned the game since few days before beta release, and have played SMP before, but it's now giving me this error for every server I attempt to join.
I also encouter this problem while trying to connect to various servers. I have yet to connect succesfully (meaning it has not worked for me yet). I would really appreciate if some light could be shed on this problem.
To me, this happens on both the exe and the browser version.
I've only tried 2 servers as of yet, one of them is a simple one a friend of mine made with no extra security. I don't know about the other one.
Has anyone found the fix for this? It's on my own server. I was able to get on just fine until there was a terrain glitch, so I reloaded. Now it can't verify my username.
Please read my quote. It does not matter if it is on your server or not, the fact is that your server has to contact minecraft.net which is what is creating the issue. Wait for a webserver update! It shouldn't be too long now.