Microsoft recent security update has resulted in compilation error.  After spending some time came across this link.  This is a known issue. Error: Could not load file or assembly 'System.Web.Mvc, Version=4.0.0.1, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT

Error: Attempt by security transparent method 'WebMatrix.WebData.PreApplicationStartCode.Start()' to access security critical method 'System.Web.WebPages.Razor.WebPageRazorHost.AddGlobalImport(System.String)' failed. Solution: Install Nuget Package Microsoft.AspNet.WebHelpers Example: Install-Package Microsoft.AspNet.WebHelpers

Error: Could not load file or assembly 'WebMatrix.Data, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) Solution: Install Nuget Package Microsoft.AspNet.WebPages.Data Example: Install-Package Microsoft.AspNet.WebPages.Data