Comment from Michael Paine
There is another problem with Messages - old .mac accounts. See this Apple discussion:https://discussions.apple.com/message/19054375#19054375
View ArticleComment from Adam Engst
From what I can tell from this discussion, there are problems with some old mac.com-related Apple IDs, and the only solution is to call Apple support. Unsatisfying, I know, but that's what happens with...
View Article