If you upgrade your mac to Yosemite, your yahoo messenger will not work.
All credit to Chris Knight for this fix.
Download the following patched Adium and you're good to go.
http://www.ghostwheel.com/adium-yahoo-fix/Adium.app.zip
Original post can be found here...
http://www.ghostwheel.com/merlin/Personal/notes/tag/yosemite/
-Khalid
