Installing .NET 3.5 on Windows 8.1I've recently upgraded my desktop with a shiny new SSD. I opted for the full reinstall of Windows as the easiest option. Window updates took a while, but I was able to get upgraded to Windows 8.1 eventually.
Unfortunately the next day I encountered a problem getting .NET 3.5 installed. The normal installers don't work because this is now a Windows Feature, but adding the feaure would always fail. After several different attempts at a fix, including trying to install from the command line via the original DVD I found a serverfault post here which suggested uninstalling two updates KB2966826 and KB2966828. After these were removed the install worked.
I don't know for certain that this was definitely the fix as I also did a disk cleanup which removed Windows.old which was the old Windows 8.0 directory. Both options are worth exploring.