I downloaded Tonfotos today and it installed smoothly. I have no information on what changed. I can tell you the steps I took because they may have helped.
I contacted Avast Support (via their Download page) and was directed to their Forum where I explained the problem (user1938). A Leader of the forum responded quickly with directions for using the Avast debugging tool. I don’t think it will help anyone to repeat that long conversation here, but I followed those directions. I checked back frequently at first with no change, but today the download and installation was smooth.