What are you experiencing? Is it only in Chatrooms. I also had a problem with my YM cos it always says Signing in as bla bla bla.... but it's only up to that then I could no longer see my contacts cos it had encountered Signing-in problems.. Have you tried that thing also?
I think what pinpointcomm was trying to say was that try making an alternative username that'll make things a lot more easier for you
You can also try updating your Yahoo Messenger or try to re-install it. If even re-starting your pc won't work. You can also try to check your connection preferences. Hope this helps you.
Sometimes yahoo restrisct your id from chat , the only reason is that someone complaign againt you that you broken the Yahoo terms and services. Yahoo ban your account for that.