Razor @helper in App_Code cannot be accessed

I ran into this exact problem when deploying the site onto another server. Make sure the App_Code/Formatter.cshtml file is actually copied to the server! My mistake was the file has a build action that was set to 'None'. Right click on the file and select Properties, and then set the Build Action to 'Content'.

NOTE:

If you don't have asp.net mvc 3/4 installed make sure the following dlls are in your bin folder.

• System.Web.Mvc
• Microsoft.Web.Infrastructure
• System.Web.Razor
• System.Web.WebPages
• System.Web.WebPages.Razor

Scott Hanselman has a blog post about what might be causing your issue. BIN Deploying ASP.NET MVC 3 with Razor to a Windows Server without MVC installed