You need to update the references to a newer version as follows:
1. Remove references:
SystemWeb.Mvc
SystemWeb.Razor
SystemWeb.WebPages
SystemWeb.WebPages.Deployment
SystemWeb.WebPages.Razor
2. Add references (Assemblies -> Extensions). Choose the system assemblies, not their CMS versions:
SystemWeb.Mvc – 4.0
SystemWeb.Razor – 2.0
SystemWeb.WebPages – 2.0
SystemWeb.WebPages.Deployment - 2.0
SystemWeb.WebPages.Razor – 2.0
3. Remove the view engine registration (not necessary for Razor views):
App_Code/Application/CMSAppBase.cs
//CMSWebFormViewEngine.RegisterViewEngine();
4. Update MVC version in the Web.Config:
<add assembly="System.Web.Mvc, Version=4.0.0.0, ...
-rm-