C# Invalid JSON Primitive Reading from Cookie

I'm using JQuery.Cookie to store a javascript object as a cookie value:

    var refinerData = {};
// Read in the current cookie if it exists:
if ($.cookie('RefinerData') != null) {
    refinerData = JSON.parse($.cookie('RefinerData'));
}
// Set new values based on the category and filter passed in
switch(category)
{
    case "topic":
        refinerData.Topic = filterVal;
        break;
    case "class":
        refinerData.ClassName = filterVal;
        break;
    case "loc":
        refinerData.Location = filterVal;
        break;
}    
// Save the cookie:
$.cookie('RefinerData', JSON.stringify(refinerData), { expires: 1, path: '/' });

When I debug in firebug, the value of the cookie value seems to be formatted correctly:

{"Topic":"Disease Prevention and Management","Location":"Hatchery Hill Clinic","ClassName":"I have Diabetes, What can I Eat?"}

I'm writing a SharePoint web part in C# that reads the cookie in and parses it:

        protected void Page_Load(object sender, EventArgs e)
    {
        HttpCookie cookie = HttpContext.Current.Request.Cookies["RefinerData"];
        if (cookie != null)
        {
            string val = cookie.Value;
            // Deserialize JSON cookie:
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            var refiners = serializer.Deserialize<Refiners>(cookie.Value);
           output.AppendLine("Deserialized Topic = " + refiners.Topic);
            output.AppendLine("Cookie exists: " + val);
        }
    }

I have a Refiners class for serializing to:

    public class Refiners
{
    public string Topic { get; set; }
    public string ClassName { get; set; }
    public string Location { get; set; }
}   

However, this code throws an "Invalid JSON Primitive" error. I can't figure out why this isn't working. One possibility is that its not reading the cookie correctly. When I print out the value of the cookie as a string, I get:

%7B%22Topic%22%3A%22Disease%20Prevention%20and%20Management%22%2C%22Class%22%3A%22Childbirth%20%26%20Parenting%202013%22%2C%22Location%22%3A%22GHC%20East%20Clinic%22%7D