asp.net mvc and json

I have the following class:

[DataContract]
public class FileUploaderResult
{
    [DataMember]
    public bool Success { get; set; }
    [DataMember]
    public string TempFileName { get; set; }

    public FileUploaderResult(bool success, string fileName, string errorMessage)
    {
        this.Success = success;
        //this.RelativeThumbnailUrl = fileName;
        //this.ErrorMessage = errorMessage;
    }
}

and following controller method:

    public JsonResult UploadFileAjax()
    {
        var result = new FileUploaderResult(false, string.Empty, string.Empty);
        try
        {
            //...
            result.Success = true;
            result.TempFileName = filename;
            return Json(result);
        }
        catch
        {
            result.Success = false;
            return Json(result);
        }
    }

on client part I try to parse this JSON :

                var objResponse = jQuery.parseJSON(response);
                alert(objResponse.TempFileName);

and it does not work. When I try to show response as is:

                alert(response);

I got the message with "litter" (

http://ru.magicscreenshot.com/jpg/e8f4D1ciAU8.html

why parseJSON does not work and how to do correctly?