Look, after much stuffing around, reading, following instructions and advice from many different sites on this issue it was not resolved on my 64 bit win 10 pro. It was finally sorted by running an inplace install via USB drive after uninstalling Avast free antivirus with the avastclear.exe file which takes you to safe made for the uninstall. While there I ran Ccleaner for the registry until there were no issues, then ran wise registry cleaner and removed all problems it found. I might add these were run in their default mode with no custom instructions. Then reboot back to normal mode and instead of downloading from avast which sends you to cnet which gives you some sort of compressed .exe file (4.8 mb) I went to filehippo.com and downloaded latest .exe file (193mb). Double clicked, let him go and hey presto, voila, successful install "You are now protected". The whole process probably took 40 minutes compared to hours of trial and failure step by step repair advice. Good Luck!!