Unable to parse JSON respone. JQUERY

when i try to get JSON from a webservice I get (status == "parsererror") Which means "Unable to parse JSON response". What am I doing wrong.

MyService.asmx:

 [WebMethod]
        public AssignmentInfo[] GetAssignmentInfo(int insId)
        {
            Proxies.ServiceRef.ServiceClient c = new Proxies.ServiceRef.ServiceClient();
            return c.GetAssignmentInfo(Id).ToArray();
        }

jquery implementation in .aspx page.

thi开发者_运维技巧s.ServiceProxy = function (serviceUrl) {
      var _I = this;
    this.serviceUrl = serviceUrl;
    this.isWcf = false;
    this.timeout = 10000;
    this.contentType = "application/json";

  this.invoke = function (method, params, callback, errorHandler) {
  var jsonData = _I.isWcf ? JSON.stringifyWcf(params) : JSON.stringify(params);

        // Service endpoint URL        
        var url = _I.serviceUrl + method;

        $.ajax({
            url: url,
            data: jsonData,
            type: "POST",
            contentType: _I.contentType,
            timeout: _I.timeout,
            dataType: "serviceproxy",  // custom type to avoid double parse
            dataFilter: function (jsonString, type) {
                if (type == "serviceproxy") {
                    // Use json library so we can fix up dates        
                    var res = JSON.parseWithDate(jsonString);
                    if (res && res.hasOwnProperty("d"))
                        res = res.d;
                    return res;
                }
                return jsonString;
            },
            success: function (result) {
                if (callback)
                    callback(result);
            },
            error: function (xhr, status) {
                var err = null;
                if (xhr.readyState == 4) {
                    var res = xhr.responseText;
                    if (res && res.charAt(0) == '{' && status != "parsererror")
                        var err = JSON.parse(res);
                    if (!err) {
                        if (xhr.status && xhr.status != 200)
                            err = new CallbackException(xhr.status + " " + xhr.statusText);
                        else {
                            if (status == "parsererror")
                                status = "Unable to parse JSON response.";
                            else if (status == "timeout")
                                status = "Request timed out.";
                            else if (status == "error")
                                status = "Unknown error";
                            err = new CallbackException("Callback Error: " + status);
                        }
                        err.detail = res;
                    }
                }
                if (!err)
                    err = new CallbackException("Callback Error: " + status);

                if (errorHandler)
                    errorHandler(err, _I, xhr);
            }
        });
    }
}


var serviceUrl = "service/MyService.asmx/";
var proxy = new ServiceProxy(serviceUrl);

 function showAssignInfo() {

            proxy.invoke("GetAssignmentInfo",
            { insId: $("#IAssignmentId").val() },
             function (result) {              
                    $.each(result, function (index) {

                  alert (this.ClaimId);

                 });
             }, onPageError);

Update 1:

JSON Response :

{"d":[{"__type":"Proxies.AFARServiceRef.AssignmentInfo","ExtensionData":{},"AssignDate":"\/Date(1317748587667)\/","AssignFileName":null,"ClaimId":"PA026195","ClaimantName":"Rachel Weiss","FirstContactDate":"\/Date(1302678000000)\/","FirstContactTime":{"Ticks":433800000000,"Days":0,"Hours":12,"Milliseconds":0,"Minutes":3,"Seconds":0,"TotalDays":0.50208333333333333,"TotalHours":12.049999999999999,"TotalMilliseconds":43380000,"TotalMinutes":723,"TotalSeconds":43380},"Id":5257,"InspectionDate":"\/Date(1302246000000)\/","StatusId":1,"SubmittedCount":5,"UploadedCount":9}]}

try

 [WebMethod]
 [WebGet(ResponseFormat=WebMessageFormat.Json)]
        public AssignmentInfo[] GetAssignmentInfo(int insId)
        {
          Proxies.ServiceRef.ServiceClient c = new Proxies.ServiceRef.ServiceClient();
          return c.GetAssignmentInfo(Id).ToArray();

        }