I copied toolkit\samples to C:\samples. I get the error when I open a command prompt from C:\samples\SOP and run:
set MSVCDir=C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC
"C:\Program Files\Side Effects Software\Houdini 16.0.504.10\bin\hcustom.exe" SOP_Star.C
I confirmed that the VC directory path is correct and does exist on my HD. I've tried several variations on the MSVCDir value, including backward slashes, a trailing slash, and shortened directory names.
set MSVCDir=C:/Program Files (x86)/Microsoft Visual Studio 14.0/VC
set MSVCDir=C:/PROGRA~2/MI0E91~1.0/VC
set MSVCDir=C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC
set MSVCDir=C:\PROGRA~2\MI0E91~1.0\VC
Any idea what I'm missing?