I have had this error issue since v .77. Upgrading to the beta versions fixed it but it's back with v .81.
It comes and goes; very odd. I launched the Yahoo Messenger program and was able to connect, created new preferences and when I added my Yahoo account, I got the gaim error again.
Now here's the oddest thing. I quit Adium and launched Yahoo Messenger. Then I launched Adium to see how to spell GAIM and I got the message from YM that I had signed on from a different location adn I was signed on to Yahoo via Adium.
Seems to be a possible bug, eh? But this bug was not present in the beta versions.