public JsonResult ExistUsername(string username)
        {
            var member = _memberManager.MakeInstance();
            member.Username = username;
            var status = _memberService.Validate(member);
            var data = new AjaxMessage();

            if (status == MembershipCreateStatus.Success)
            {
                data.Message = "username is avaiable";
                data.Success = true;
            }
            else
            {
                data.Message = AccountValidation.ErrorCodeToString(status);
                data.Success = false;
            }

            var result = new JsonResult();
            result.Data = data;
            result.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
            return result;
        }