Why I get the following error at begin running VS.NET 2015 debug IIS :
Attempt by security transparent method 'WebMatrix.WebData.PreApplicationStartCode.Start()' to access security critical method 'System.Web.WebPages.Razor.WebPageRazorHost.AddGlobalImport(System.String)' failed
It seem to you don't have Microsoft.AspNET.WebHelpers installed after updating from MVC4 to MVC5.
Install-Package Microsoft.AspNET.WebHelpers