无法读取null的属性“成功”

我有以下javascript函数

$("#formLogin").submit(function(e){     
       e.preventDefault();

        var memberUserName = $(this).find("#memberUserName").val();
        var memberOldPassword = $(this).find("#memberOldPassword").val();
        alert(memberUserName);
        alert(memberOldPassword);
        var obj = {memberUserName: memberUserName, memberOldPassword: memberOldPassword};
        var url = $(this).attr("action");
        $.post(url, obj, function(r){

            if(r.success) window.location.replace('http://www.example.org/memberAccount/memberDashboard');

            else  $('#errorMessageTop').fadeIn();

        }, 'json')
   })

当我发出警报时，memberOldPassword变得不确定。在我的表格中，我已归档，这是代码：

<input type="password" class="good_input" id="memberOldPassword" name="memberOldPassword" style="float:right;width:135px;"/><br />

这是我的控制器的PHP代码：

 public function loginCheck()
    {     
        // set the validation rules
        $this->form_validation->set_rules('memberUserName', 'Username', 'required|trim|encode_php_tags');
        $this->form_validation->set_rules('memberOldPassword', 'Password', 'required|trim|encode_php_tags');
        $this->form_validation->set_error_delimiters('<br /><p class=jsdiserr>', '</p><br />');
        // if validation is passed

        if ($this->form_validation->run() != FALSE) 
        {


            $this->db->where('memberUserName', $this->input->post('memberUserName'));
            $this->db->where('memberOldPassword', strtoupper(md5("EBOSS/".$this->input->post('memberOldPassword')."/EBOSS")));
            $query = $this->membersModel->get();
            if($query)
            {

                $data = array(
                    'memberID'                      => $query[0]['memberID'],
                    'memberUserName'                => $query[0]['memberUserName'],
                    'memberOldPassword'             => $query[0]['memberOldPassword'],
                    'memberEmail'                   => $query[0]['memberEmail'],
                    'isUserLoggedIn' => TRUE
                );           
                $members = $query->result_array();            
                $this->session->set_userdata('currentMember',$data);

                echo json_encode(array("success" => true));
        } else {   
                echo json_encode(array("success" => false, "error" => "Wrong credentials"));
        }
        //  form validation has failed 
        } else {     
            $errorMessage = "Wrong Username or passwrod!";
        }
    }   // end of function loginCheck 

我使用jQuery v1.7.2，PHP版本为5.39

有人知道更改密码后为什么我不确定吗？