Visual Studio: The Windows SDK version 8.1 was not found. Install the required version of Windows SDK or change the SDK version in the project
I encountered this issue when trying to compile some old code. I tried to download the SDK, but there are no active links. My resolution was to install Visual C++' support in Visual Studio 2015 by re-running the installer. Its like killing a fly with a hand-grenade (3GB install), but as least it resolved the problem.