System.Web.Mvc.HtmlHelper does not contain a definition for 'Syncfusion' Error

I'm working with ASP.Net MVC 3 with the Razor engine and version 9.104.0.20 of the SyncFusion mvc control suite.

In the documentation for this control, I am to put lines of code similar to the below in my master page:

@Html.Syncfusion().ScriptManager()

Per the Syncfusion documentation and this Stack Overflow suggestion, I have made sure to add the namespaces to my web.config file under the element.

The solution builds but I get the following error when I run it:

'System.Web.Mvc.HtmlHelper' does not contain a definition for 'Syncfusion' and no extension method 'Syncfusion' accepting a first argument of type 'System.Web.Mvc.HtmlHelper' could be found (are you missing a using directive or an assembly reference?)

I don't think this issue has to do with Syncfusion but instead with my inability to reference their assemblies correctly.

How do I address this?