https://www.dotnetzone.gr:443/cs/blogs/birbilis/archive/2015/11/23/howto-reinstall-a-new-windows-10-build-after-reverting-to-older-build.aspxAt http://www.askvg.com/fix-windows-10-insider-preview-build-10240-not-appearing-on-windows-update/ it writes: NOTE: If you previously had a new Windows 10 build installed in your computer and then reverted back to an older build, you’ll lose accesselCommunityServer 2.1 SP3 (Build: 20423.1)