Last month Oracle closed some security loop holes in Java that resulted in many users applying Java release 6 update 33 through Java release 7 update 5 being unable to access their chat rooms, including those using addonchat like Thom's. Procedures to fix the problem have been posted on the web in various forums, which must be performed by every individual user after they update Java and find they can no longer access chat.
The error message that I received because of this problem after installing Java 7 upd 5 was the following (the error message you receive may be different, but the procedures may fix your problem also) :
Unsigned application requesting unrestricted access to system
Unsigned resource: http://client0.addonchat.com/current/AddonChat_signed_en.jar
Please note, this problem affects Mac users in addition to Windows users, and may also affect Linux users ... it also affected users of several different browsers, including Chrome and IE, which I use. I was unlucky enough to follow harry ashburn into that black-hole that is known as the "chat-free zone", until i found instructions on the 'net posted by a techie for another chat forum (Thank you very, very much, Greg ! ... see below for a link to his comments). The fix is really quite easy, and involves a couple of little cleanup tasks, including deleting the Java cache, and can be done in 5-10 minutes.
Well, this thing bit another of the Thom Hartmann chatters on the night of 7/9/12 ... poor art. I tried to direct him to my last reply in harry's post which is where he can find the solution, but it seems that is too clumsy. So, I'll copy it to this post, and attach it as the first reply ( it is reply #7 in harry's post, with an update time stamp of 17. June 2012 - 13:18 ) .
Harry and Art were able to fall back to an earlier Java release, Java 6 update 32 i think, as a temporary measure ... links for finding these older releases are in the posts.
A link to harry ashburns original post will be placed here, for those who want to read the history of this problem, or like to read the ramblings of chat addicts going through withdrawal (well, ... i missed the gang).
Here is a link to the post where Greg included his instructions; you may find some of the other comments useful in addressing the problem you are experiencing now or in the future :