This build error popped up after updating Nuget packages. There is lots of info out there about Error CS5001, but nothing regarding this error in UWP that I can find.
The error references folder \Visual Studio 2015\Repos\MySolution\MyProject\CSC. This folder does not exist, but it doesn't exist in any of my other UWP apps either and they build just fine.
Rebuild, Clean, restart VS, no fix.