I am following this article on RazorGenerator and it say\'s that I must add references to:
System.Web.Helpers.dll
System.Web.WebPag
They should be under C:\Program Files\Microsoft ASP.Net (or C:\Program Files (x86)\Microsoft ASP.Net if you're on a 64-bit OS) in a subfolder for MVC3 or WebPages.
C:\Program Files\Microsoft ASP.Net
C:\Program Files (x86)\Microsoft ASP.Net