I have the same problem between Autocad and the Avast version 17.1.2286 (windows 7). The actual problem is that I can’t open a new file with Autocad because the program due to Avast malefactions. I have tried all the other free antivirus programs and I don’t have this problem but I prefer Avast because I use it for many years and I know that it is a trusted antivirus although it’s free. Does anyone have the solution? I have already tried the solution with the registry file that someone wrote above but it is not working!