Have a private blog, and used Quick Chat successfully for several weeks; then it just stopped working. I have few plugins: Private Only, WP Firewall 2, WP-MalWatch, WP Security Scan, WPtouch.
When I load the page (it piggybacks on a wp page), I see some text for a split second, then it's blank and never comes back; the experience is the same for all users. From reading threads, I'm guessing it's a conflict with another plugin, but the security plugins not negotiable, so I'll look for another chat plugin.