回答ありがとうございます
s_gotoさま。
FFFTPで接続し、
data/eccube/data/class_extends/page_extends/admin/order/LC_Page_Admin_Order_Edit_Ex.php
を開いてみたら
<?php
/*
* This file is part of EC-CUBE
*
* Copyright(c) 2000-2012 LOCKON CO.,LTD. All Rights Reserved.
*
* http://www.lockon.co.jp/
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/

// {{{ requires
require_once CLASS_REALDIR . 'pages/admin/order/LC_Page_Admin_Order_Edit.php';

/**
* 受注修正 のページクラス(拡張).
*
* LC_Page_Admin_Order_Edit をカスタマイズする場合はこのクラスを編集する.
*
* @package Page
* @author LOCKON CO.,LTD.
* @version $Id: LC_Page_Admin_Order_Edit_Ex.php 21867 2012-05-30 07:37:01Z nakanishi $
*/
class LC_Page_Admin_Order_Edit_Ex extends LC_Page_Admin_Order_Edit {

// }}}
// {{{ functions

/**
* Page を初期化する.
*
* @return void
*/
function init() {
parent::init();
}

/**
* Page のプロセス.
*
* @return void
*/
function process() {
parent::process();
}

/**
* デストラクタ.
*
* @return void
*/
function destroy() {
parent::destroy();
}
}
と書いてあり、mtb_countryはありませんでした。
どうしたら良いでしょうか？