Barry, if you are getting as far as the grey screen, it is still my guess that a security setting on your computer is the most likely cause. After you have loaded (or got as far as you can), you can view the Java Console (from Explorer - where you entred the chat - not from the Mudcat Chat page).I can get in OK but it still reports 1 exception (String index out of bounds)when I try to refresh that page. Have a look. Don't worry if it does not make any sense - just see if it reports any security Exceptions - if it does, changing your browser settings might be the answer.
Jon