Hi swelborn,
I had the same problem with [ui_user_silent] and after many days I eventually found the source of the problem! Login as Admin and under Chat Admin, choose Room Administration. Make sure "Public" is ticked and apply changes. This setting must be ticked for every room. All your users can now exchange messages :)
I also have set Private Chat to false yet users can still select it. I think this is a bug by the looks of things. You'll find disabling "Show Room list" also fails to work and I think Adam has confirmed this as a bug already.
I have a similar problem whereby all my rooms are passworded and I have enabled IP filtering, but right clicking the dialogue area allows a moderator to "Allow Anonymous Users", but it doesn't appear to do anything. Maybe this is another bug?
Mike