Shoutbox

I've always had this problem, when contacts leave or get invited into a conversation, the whole msn screen will go blank and lag for a very long period of time. I got Norton Antivirus installed, is it because of its auto-protect function? I found out from my friends that they dont lag when contacts got invited or left a conversation. Everytime I try to close the chat window, there will be a "Program not responding" pop up, and I often have to restart MSN if it crashes. I cant enjoy mass convos like this