what is the error message you receive? check for your connection or you can try re installing it. reinstalling does help in such situations.
I also have YM problem... I can't add friends for 5 months now. I don't know whats up with that and I have given up figuring out what to do... Sigh...
what error are you getting? Have you tried to login with your Mail Account using the same account that your using to your YM? Where you able to login successfully?