this is common error of MSI installation process and to check the culprit, it is needed to analyze installation log. Please follow the steps from this AVG Free Forum How-To article - http://forums.avg.com/ww-en/avg-free-forum?sec=thread&act=show&id=85955 - and upload needed MSI file to favorite online storage for closer analysis.
I have downloaded the free version of AVG 2011, but when I try to install it I get the following message
error code 0xC0070643 fatal error during installation. MSI engine: failed to install the product.
I am using Windows XP.
Hope someone can help me.