There is a minor syntax error that appears to have significant impact on submitting questions.

I found that the file tpl_faqs_submit_default is missing the first ?>

See below:

<?php
//
// +----------------------------------------------------------------------+
// |zen-cart Open Source E-commerce |
// +----------------------------------------------------------------------+
// | Copyright (c) 2003 The zen-cart developers |
// | |
// | http://www.zen-cart.com/index.php |
// | |
// | Portions Copyright (c) 2003 osCommerce |
// +----------------------------------------------------------------------+
// | This source file is subject to version 2.0 of the GPL license, |
// | that is bundled with this package in the file LICENSE, and is |
// | available through the world-wide-web at the following url: |
// | http://www.zen-cart.com/license/2_0.txt. |
// | If you did not receive a copy of the zen-cart license and are unable |
// | to obtain it through the world-wide-web, please send a note to |
// | [email protected] so we can mail you a copy immediately. |
// +----------------------------------------------------------------------+
// Original contrib by Vijay Immanuel for osCommerce, converted to zen by [email protected] - http://www.open-operations.com
// $Id: links_manager.php 2004-11-19 [email protected]
//?>

Without the ?> you get an error when posting question and then a guest greeting screen appears.