Right now, my results were:

http://www.asw.cz/iavs4pro (IP: 195.70.130.34) > 100% loss

The others works perfectly without any loss:
http://www.avast.com/iavs4pro (IP: 64.246.6.135)
http://www.iavs.net/iavs4pro (IP: 207.44.156.15)
http://www.iavs.cz/iavs4pro (IP: 62.168.45.69)

I use Windows XP Pro SP1, ZoneAlarm and XP firewall in ON.
So, I think you have a trouble with your connection… Maybe you can uninstall and install avast again but I can’t think what is going on… :-\