if it is a legal stuff, then send it as an attachment to virus[at]avast[dot]com and describe it shortly… we’ll remove the false detection and add the file to our cleanset…
As a workaround, you can add these files to the Standard Shield provider (on-access scanning) exclusion list.
Left click the ‘a’ blue icon, click on the provider icon at left and then Customize. Go to Advanced tab and click on Add button…
You can use wildcards like * and ?. But be carefull, you should ‘exclude’ that many files that let your system in danger.