same problem...
the first problem was in chrome after the opening chat window the browser gave error "The requested URL/....blank.php was not found" I went to FTP and found this file, but "blank.html", I renamed him to .php, after that problem wasn't appear, BUT bottom "sent" doesn't work and as a result I can't sent messages. I checked all buttons in window: don't works buttons "sent" "close" and "refresh history" other buttons work correct. If I just open window and sent any message from admin panel, user dosen't see the message.
The strange is, as I understand user's chat-window and admin's chat-window are similar, but if I work through Chrome as Admin - it work correct(all buttons work, sent, and I can see messages on chat), but if I open chat-window as user it doesn't work.