You could send a false positive report without attaching a sample, basically a copy of your first post with a little more info, like the actual file name (installer, patch or otherwise) send it to virus @ avast.com (without the spaces).
If you are happy that you believe it is a false positive, you could exclude the file from scans until it is corrected.
If it is indeed a false positive, add it to the exclusions lists:
Standard Shield, Customize, Advanced, Add and
Program Settings, Exclusions
Periodically check it (scan it, or visit the site) and see if it is still detected. When it is no longer detected then you can also remove it from the Standard Shield and Program Settings, exclusions.