chat in separate window function

Hi all, 
 
The chat in separate window function doesn't work in my installation: http://kowalskymegavega.hu/chat
 
When a chatter choose somebody and initiate a private chat, the other people get a notification from this and a separate window is opened ont he other side. There is no error message. Everything looks fine, but the messages don't appear for each other.  
 
Could you tell me, please whether in other installation this function works or not? 
 
Is there any idea how can I solve this or what should I try? 

I am using PhpOpenChat version 3.0.1 with MySQL database 2.5.1

 
Thank you in advance! 
Peter