|That would be a yahoo problem, you could start by contacting them.|
It also sounds like a java issue. Go to your control panel and update your java and see if that works for you.
Just a suggestion, you may want to try free pogo pool, IMO it is much better than yahoo pool as it is in 3d and works great. You don't have to be a club member to play it.
Some HELP in posting on Computing.net plus free progs and instructions Cheers