Hello,
I am suffering from exactly the same issue. One day, both WWW and e-mail stopped working on my home XP machine. Only what the browser has in its cache was used, the transfer appeared as finished but it behaves as if it was empty.
It took me a considerable time to find the source because of another issue I believed was the cause. I took the windows FW for guilty, I repaired windows, moved to another disk ... installed the Sunbelt personal (ex-kerio) firewall... and stopped the MS one.
I finally checked in case a strange setting was in place in AVAST and found that if I prevent the WEB documents from being scanned or if I inactivate the WEB shield, then it works fine :-(
I tried re-installing AVAST with no change.
Note that I have a pro version on a business machine that does not show that issue.
Is there a chance that it is fixed soon in a next release?