既存のページを入れ替えて表示可能なソース

<?php
namespace Plugin\Custom\Controller\Admin;

use Eccube\Application;
use Symfony\Component\HttpFoundation\Request;
use Plugin\Custom\Common\CommonUploader;
use Plugin\Custom\Common\S3NoViewBacketCommandFactory;

class FeeFreeController
{
    public function index(Application $app, Request $request){
        $builder = $app['form.factory']->createBuilder('admin_payment_maint');
        $form = $builder->getForm();
        $form->handleRequest($request);



        return $app->render('Custom/Resource/template/admin/Maint/payment_maint.twig', array(
            'form' => $form->createView(),
        ));
    }
}

テスト環境でエラーが出ている状態のソース
<?php
namespace Plugin\Custom\Controller\Admin;

use Eccube\Application;
use Symfony\Component\HttpFoundation\Request;
use Plugin\Custom\Common\CommonUploader;
use Plugin\Custom\Common\S3NoViewBacketCommandFactory;

class FeeFreeController
{

    public function index(Application $app, Request $request){
        $builder = $app['form.factory']->createBuilder('admin_fee_free');
        $form = $builder->getForm();
        $form->handleRequest($request);

        return $app->render('Custom/Resource/template/admin/free/fee_free.twig', array(
            'form' => $form->createView(),
        ));
    }
}

fee_free.twigの中身です。
{#
This file is part of EC-CUBE

Copyright(c) 2000-2015 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.
#}
{% extends 'default_frame.twig' %}

{% set menus = ['setting', 'shop', 'fee_free'] %}

{% block title %}基本情報設定{% endblock %}
{% block sub_title %}手数料設定{% endblock %}

{% form_theme form 'Form/bootstrap_3_horizontal_layout.html.twig' %}


{% block stylesheet %}
{% endblock stylesheet %}

{% block javascript %}
{% endblock javascript %}

{% block main %}
<div class="row" id="aside_wrap">
    <form name="form" method="post" action="?">

    </form>
</div>
{% endblock %}