FireFox/Avast agony

I'm using the free antivirus Avast! on this computer and recently suddenly started receiving a lot of strange error messages. It comes up in red and reads:

The page cannot be displayed
There is a problem with the page you are trying to reach and it cannot be displayed.

Please try the following:

    * Click the Refresh button, or try again later.
    * Open the Web site home page, and then look for links to the information you want.
    * Check your firewall settings. The Web Shield process (ashWebSv.exe) must be allowed to access the Internet.
    * If you believe you should be able to view this directory or page, please contact the Web site administrator by using the e-mail address or phone number listed on the Web site home page.

HTTP 502 - Gateway timeout
avast! Web Proxy

The proxy server did not receive a correct response from the upstream server specified by URI or the response was not understood by proxy.

Winsock: (997) Overlapped I/O operation is in progress.
GET {this is the url at the time}
Winsock: (997) Overlapped I/O operation is in progress.

I have yet to find any useful information toward resolving this issue. Seems like it goes away if I go to "On-Access Protection Control" and disable Web Shield. I didn't even know I was using a "web proxy" on this machine. Could explain some of the sluggishness.