WordPress logs out after using /wp-admin/admin.php - wordpress

Question

i'm currently updating a system with a new function. I'm adding the show_user_profile and edit_user_profile action to add custom data into the user-view:
<script type="text/javascript">
function bindRemoveButton() {
jQuery(function($) {
$('table.available-users button.remove').on('click', function() {
$(this).parent().parent().remove();
});
});
}
bindRemoveButton();
</script>
<table class="form-table available-users">
<tbody>
<tr>
<th>
<label for="accounts"><?php print __('Assigned accounts', ZVA_I18N); ?></label>
<br />
<br />
<a href="<?php bloginfo('template_directory'); ?>/templates/admin/user_add_box.php#TB_iframe=true&width=600&height=550" title="<?php print __('Add User', ZVA_I18N); ?>" class="thickbox button button-primary"><?php print __('Add', ZVA_I18N); ?></button>
</th>
<td>
<table class="wp-list-table widefat fixed users">
<thead>
<tr>
<th scope="col" class="manage-colum" style="padding-left: 20px;"><span><?php print __('Username', ZVA_I18N); ?></span></th>
<th scope="col" class="manage-colum"><span><?php print __('Date From', ZVA_I18N); ?></span></th>
<th scope="col" class="manage-colum"><span><?php print __('Date To', ZVA_I18N); ?></span></th>
<th scope="col" class="manage-colum"><span><?php print __('Action', ZVA_I18N); ?></span></th>
</tr>
</thead>
<tbody>
<?php
foreach($user_available AS $aindex => $available_user) {
$user = new WP_User($available_user['user_id']);
?>
<tr>
<td><?php print $user->user_login; ?> (<?php print $user->display_name; ?>)</td>
<td>
<input type="text" name="jumper_day_from[<?php print $user->ID; ?>]" size="2" value="<?php print date('d', $available_user['from']); ?>" placeholder="DD" />.
<input type="text" name="jumper_month_from[<?php print $user->ID; ?>]" size="2" value="<?php print date('m', $available_user['from']); ?>" placeholder="MM" />.
<input type="text" name="jumper_year_from[<?php print $user->ID; ?>]" size="4" value="<?php print date('Y', $available_user['from']); ?>" placeholder="YYYY" />
</td>
<td>
<input type="text" name="jumper_day_to[<?php print $user->ID; ?>]" size="2" value="<?php print date('d', $available_user['to']); ?>" placeholder="DD" />.
<input type="text" name="jumper_month_to[<?php print $user->ID; ?>]" size="2" value="<?php print date('m', $available_user['to']); ?>" placeholder="MM" />.
<input type="text" name="jumper_year_to[<?php print $user->ID; ?>]" size="4" value="<?php print date('Y', $available_user['to']); ?>" placeholder="YYYY" />
</td>
<td>
<button type="button" class="remove button button-primary"><?php print __('Remove', ZVA_I18N); ?></button>
</td>
</tr>
<?php
}
?>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
Okay, no problems. See the Line 19 on my code, here i add a Link/Button to open a new Thickbox with additional content. When i click on the link, a thickbox pops up and displays the content from the File /wp-content/themes/MyTheme/templates/admin/user_add_box.php.
To use WordPress's own functions (like $wpdb or other), im including the admin.php on the user_add_box.php - YES, currently that's only these line on the file:
<?php
define('WP_ADMIN', true);
/* Nativate to /wp-admin/ directory */
require_once(dirname(dirname(dirname(dirname(dirname(dirname(__FILE__)))))) . '/wp-admin/admin.php');
?>
When i'm open the tickbox, the login will be shown - curiously. After that i'm complete logged out from WordPress.
I work very very long with WordPress and never had such problems. Especially since I also developing for years themes and plugins for WordPress.
Can you tell me, what i'm doing wrong? Why the system logs me out?
Thanks for your help.
EDIT
After see the core file, i see i must define constants like define('WP_ADMIN', true);, but thats dont solve the problem.

Answer 1

In the auth_redirect method (wp-includes/pluggable.php) will be checked if the file comes from wp-admin directory:
if ( $secure && !is_ssl() && false !== strpos($_SERVER['REQUEST_URI'], 'wp-admin') )
If not, the system will be redirect automatical to the wp-login.php.
Solve it to rewrite the $_SERVER['REQUEST_URI'] variable:
<?php
$_SERVER['REQUEST_URI'] = 'wp-admin';
require_once(dirname(dirname(dirname(dirname(dirname(dirname(__FILE__)))))) . '/wp-admin/admin.php');
?>
Otherwise, add only wp-load.php and wp-admin/includes/admin.php:
<?php
$_SERVER['REQUEST_URI'] = $_SERVER['HTTP_REFERER'];
require_once(dirname(dirname(dirname(dirname(dirname(dirname(__FILE__)))))) . '/wp-load.php');
require_once(dirname(dirname(dirname(dirname(dirname(dirname(__FILE__)))))) . '/wp-admin/includes/admin.php');
?>