I have a simmular problem. First login works and shows turtorial. After Turtorial screen says: "unexpected disconnect from online services. Please check your internet connection."
Tried everything I know, turning fire-wall and antivirus off didn't work as well.
Ther are no problems with my internet. All works well, except for C&C4.
I see this problem was already posted, but I don't see a solution on the forum???