asp.net - Basic Compilation Issue - missing a using directive or assembly reference -

I have found the following code with the web and trying to compile and run it. One of its AJAX applications could not get it to compile / create this application because it returns the following error:

Are not you in use directory or assembly reference

Can someone give advice / what should I check?

Code here Ajax Controller CS; And the word controller is underlined:

  Namespace system. Web.Mvc {Public Class AjaxController: Controller {Private bool _isAjaxRequest; Protected Internal Virtual Boolean IXXEquest {get {return_isAjaxRequest; }}}}}  

Check that the system in the project. Extension Assemblies.