[jQuery] JQuery Flot, beginners problem

[83nini]

Hi all,
I'm an absolute beginner in JQuery, and i need your kind help on
this...
i have an mvc project in asp.net, visual studio 2010
i added the jquery.js and jquery.flot.js files in the master page,
then i went to HomeController.cs and wrote the following method:

public ActionResult Example()
        {
            string s = "[[2003,10882],[2002,10383],[2001,10020],
[2000, 9213]]";
            return Json(s, JsonRequestBehavior.AllowGet);
        }

as you see i'm trying to get json object..
so in the Index.aspx i wrote the following javascript code

$(function () {
            $.getJSON("../../Home/JsonValues/", function (data) {
                var plotarea = $("#plot_area");
                $.plot(plotarea, data);
            });
        });

problem is i'm getting an empty graph, i.e. data = null
i'm tracing with the firebug, and seems the problem is context =
undefined!

how do i solve this?
i've been googling the whole morning but in vain!!!