I have two accounts on my mac. The first configured account still works. However when i logon to the other account on my mac and i start using facetime on that account I get the exact same error as you describe above.
These questions are asked long back by I pad users ,but this i pad support team is not giving proper answer to me ,they r cheater ,just they r sending me to community and find the answer yourself. They r playing with the customers,by not giving