Open up Java Control Panel under Start Menu\All Programs\Java\Configure Java
Go to the security tab on the Java Control Panel and click the "edit site list" button. Then under "location," type (or cut and paste) the following two exceptions into the list one at a time and click "add:"
You will get a warning that http is not recommended and it will recommend using an https site... but just hit ok.
That should get you all back online for chat.