When I open the chat window now, it actually works just fine for me.. And I haven't updated IE or Windows XP in any special way since the last time I tried to open it (and failed)... So unfortunately, I can't say that I have any clues to why this works for me now.
But I did send the HTML source to Cutesoft, just as Adam requested, so I guess that there's a possibility that they have updated the application on the demo site. Can you open a chat room window on the demo site?
BTW: I still get the same error when i try to open the Messenger window on the demo site. So I still have problems..
Regards,
/Magnus