A: 

Just throwing some ideas out there...

http://www.asp.net/learn/MVC/tutorial-33-cs.aspx

Your controller action is in a class defined like so?

public class MyController : Controller

Apparently the name of the class has to end with the word controller.

rvarcher
I'm using the default HomeController so yes, it is called HomeController and extends Controller.
Martin Doms
+4  A: 

You have the javascript include in your master page in the wrong order. Reorder so that MicrosoftAjax.js is included first of the three and it will work.

<script src="../../Scripts/MicrosoftAjax.js" type="text/javascript"></script>
<script src="../../Scripts/MicrosoftMvcAjax.js" type="text/javascript"></script>
Jesper Palm