I appreciate your response. Thank you. Here is my response to your questions and suggestions:
I have version 4.8 Home Edition. I initially installed it on June 9th, 2008. It was working fine all the way till about four or five days ago when this error started coming up. I have no other Anti-Virus software installed, and I uninstalled the one I had before installing avast on June 9th, which I must have done properly because avast worked fine for the rest of the month. I do not have Zone Alarm, or any other firewall software, and I do not have the Windows firewall turned on, because I have a router where I setup which incoming ports I want open. The outgoing ports are all open. I also have not installed any new software since the time when avast was working.
I do a manual update and the download does start, but then stops at the exact same byte-count 180,224 out of 340,301 bytes every time. When this problem first started, it also stopped at 180,224 bytes out of xxx bytes where xxx was a smaller amount, so I assume there is more to download now then there was the first day this problem started.