Got Chat working on my desktop (IE, FireFox and Chrome).
Had to go to the Control Panel on my PC. In the Control Panel Search box, typed "JAVA". Opened Java which brought up the Java Control Panel.
Under the Security Tab, had to check "Enable Java content in the browser." Then Apply.
After I did that, I had to open all three browsers and go into Chat. All three asked to to enable the ChatAddOn.
So Stewart was spot-on (nothing new there): this is a Java Configuration issue.
I'm just not sure what changed from last week when I was able to get into the Chat room. .