FaceTime "Error Occurred During Activation" What is that?

Trying to log in from MacBook, yes, using correct ID and password. Checked many times- Network connection is fine-check that off the list too. Restarted computer multiple times-check off the diagnostic list. So, what is the problem exactly? Why can we not log in, and instead get message that "an error occurred during activation. Please try again"? Ridiculous.