Ehm, what is this?

I keep getting this error while trying to connect to the server.
I managed to get on and login without problems after a while, but now it pops up again.
MC.net is up, and I see three people online.

Looks like some kinda client error to me. try re downloading the game or deleting the jar.

I've gotten this message whenever MC has frozen up, I've closed it using Windows Task Manager, then reopened and tried to log back in. I think what happens is MC.net still thinks you're logged in. It went away after a few minutes for me.

I suppose whatever it is, it hasn't come back like I tought it would do.

And for me it never froze, I could just click cancel and try again.