Can someone please explain why I can't use the one apple id to remain signed in to imessaged and facetime?

After updating to MountainLion my previously unbridled enthusiasm for being able to imessage and FaceTime my friends has been utteraly butchered by the temperamental nature of both programs and the limited help offered. I did manage to get iMessage up and running but after re-setting my password in a bid to use facetime iMessages has since ceased to operate. This is so infuriating! What can i do to remedy the situation? Must i really choose?

It seems so, and live with this message "The server encountered an error processing registration. Please try again later."

Try again later? Why, whatever might have changed? So irritating and unhelpful.

I really am at a loss here.