Yup I'm getting the same thing. I just signed off utopia to go to smp6 and got this error. I restarted MC and still no change.
I removed picture from post as thats actually sensitive information you don't want the public to have. I believe mojang might of fixed some security holes with it, but still don't want to take chances.
I.HATE.PEOPLE.WHO SPEND ALL THEIR TIME FIXING OTHER STUFF THAN WHAT NEEDS TO BE FIXED. CURSE YOU JEB!!
seems like this is a problem just for someone since i logged out of utopia got the same massage, waited 5 min and now im in again