I have tried 3 times w/Avast! Free antivirus NU 2016 and every time failed.It restore windows8.1 again and again.Then i decided that i am going to uninstall avast! and install Windows10.And it went fine without Avast! NU 2016.Then reinstalled Avast! NU again in windows10.BTW it is a stable Windows10.Is there any issue with upgrade windows10?
Yes ,there is some issue with the upgrade on latest version. We are looking into it.
Thanks for clarification.Hope it will solved soon before free upgradation is Over(29th July).@MartinZ 
Strange, I have 2 systems on the latest build and am using Avast 12.1.2272 build 12.1.3076.6
http://screencast-o-matic.com/screenshots/u/Lh/1468322011517-34905.png
Wonder if this user is suffering from this problem ???
https://forum.avast.com/index.php?topic=188184.msg1323617#msg1323617
You have Windows10 Insider Preview.And i have this problem on windows10 stable version with Avast! Free Antivirus NU 2016(Avast 12.1.2272 build 12.1.3076.6).And avast! surely have some issues with the upgrade on latest version.And i have tried it 3 times and failed and restore with win8.1 repeatedly.
Yes he has.@Bob.Same error 0x8007002C - 0x4000D Second Boot Data Migration Errors
Ok, found the cause and fixed it. Microupdate will be released in few hours. sorry for the troubles