Thought you knew a lot more about computers than me,... but I'll give my bit of probably useless info:
Are you on dial up?
I get a box with a similar message, but with the error code of '404' EVERY time I am getting on the internet, THROUGH MY DIAL-UP. When I go to the library which has a T-2 dedicated connection, I log into MyCopper, and I never get it.
I have come to the conclusion that it just means that somewhere between my computer and Copper's servers, the 'handshake' was not processed fast enough to suit some fickle software somewhere.
But all I need do is 'X' out the error code box, and proceed as if it never was there... by that time the 'handshake' is done.
PS. I was getting this all along before The Great Rollover and still now.