Maybe I can suggest avast! that the update is begginig very "fast" with the Internet connection. Some systems may take a little to open all resources when connected to the Internet (firewall, proxy, and so on). avast! try to update before the system is completely "ready" for browsing and downloading...
I notice this in a Windows 98 with proxy...
If the user waits a little, few seconds, and try a manual update, everything goes fine...