As suggested, I have tried to add these two lines to WebShield.ini using Notepad:

[General]
UseStreamFilter=0

However, when I try to save the file with that change, first Avast tries to block that change. I say that the change is OK. But then Windows tells me that I cannot save changes to that file. Then Windows Data Execution Prevention shuts down Notepad. What can I do to successfully edit Webshield.ini?

I am on Windows Vista.

Thanks.