I am in the process of upgrading to MVC4. I have followed the instructions at http://www.asp.net/whitepapers/mvc4-release-notes#_Toc303253806 but in my Razor views and layou
I used the following article on MSDN to solve this issue (in this case from MVC 4 to MVC 5)
https://docs.microsoft.com/en-us/aspnet/mvc/overview/releases/how-to-upgrade-an-aspnet-mvc-4-and-web-api-project-to-aspnet-mvc-5-and-web-api-2
Main extracts from the article are:
In the runtime block update System.Web.Mvc to 5.0.0.0 ,System.Web.Helpers to 3.0.0.0 and System.Web.WebPages to 3.0.0.0
Then look for the appsettings block and update the webpages:Version value to 3.0.0.0
Update the host factoryType block to System.Web.Mvc to 5.0.0.0
Then under the pages block update any references to System.Web.Mvc to 5.0.0.0
And finally under the configuration block update the System.Web references to 3.0.0.0