Why does Avast... stop?

My website has a chat function that works perfectly well almost all the time. When people are running avast! however, sometimes it just… locks up. Stop/starting on-access protection makes it work again, but avast doesn’t log any errors or give any feedback whatsoever… it just locks up.

The site’s here http://www.paradoxthemusical.com

If anyone can figure out WHY avast keeps locking up, I’d be very happy to make the required changes.

Regards,
Gobberwart

It seems ok for both avast and Dr. Web.
Are you sure it’s not a firewall issue? Are that people just using Windows firewall?