I may have missed it, but I don't recall seeing anyone talk abou the 64-bit install for AVG free here. Did you try that? Here is an easy place to download it http://www.filehippo.com/download_avg_antivirus/. I have found that using the 32- or 64- but install from a full download has worked much better on the 64-bit home systems I've worked on ... though I can't explain why.
I know you were having trouble setting it up on 64-bit Windows ... I was wondering if you downloaded the setup designed for 64-bit (the link I provided has it)? I found that if I did the free link from the AVG site, it sometimes tried to install the 32-bit version of the app rather than the 64-bit version.