yes I was getting the exact same message, until my neighbour came took me round to his PC.
On his young lads screen I was being logged in automatically every time his son went on.
All sorted now and we don’t know how it happened…
I to have had this problem and reported it to Yahoo, this is what they said.
“Please be assured that we are aware of this problem and your access to
Yahoo! Messenger and Yahoo! Chat will be restored as soon as possible.
We apologize for any inconvenience this may have caused.”
My problem was only now and again