The build is failing because the reference assembly folder doesn't exist on the build agent machine. As you can see from your email I've asked Anne Epstein to install the latest SDK which should add it. Once she has done this, we might find it necessary (or preferable) to point to the 4.5.1 folder rather than 4.5, i.e. `C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5.1`