Site stopped working in asp.net System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to

Question

I have a problem like this on server

[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration

Answer 1

Ian's solution worked in one project, but for others I need the more complete info in How to Upgrade to MVC 5 and Web API 2