I get an Ajax error on Manage Display for any content type when i try to move a field to hidden group or press the gear icon for field options,
and that happens when I create a custom panel layout template
if i remove the panel template everything works fine.

Two screenshots for more clearance:
Manage Display Ajax Error with panels

files screenshot of the custom panels template

code of 'husOneColumn.inc':

<?php
/**
* implementation of hook_panels_layouts()
*/
// Plugin definition
$plugin = array(
  'title' => t('Single column by hus'),
  'category' => t('Columns: 1'),
  'icon' => 'husOneColumn.png',
  'theme' => 'husOneColumn',
  'css' => 'husOneColumn.css',
  'regions' => array('middle' => t('Middle column')),
);

code of 'husOneColumn.tpl.php':

<?php
/**
* @file
* Template for a 3 column panel layout.
*
* This template provides a very simple "one column" panel display layout.
*
* Variables:
* - $id: An optional CSS id to use for the layout.
* - $content: An array of content, each item in the array is keyed to one
*   panel of the layout. This layout supports the following sections:
*   $content['middle']: The only panel in the layout.
*/
?>

   <!-- Begins panels-onecol.tpl.php by hus-->
    <?php print $content['middle']; ?>
<!-- Ends panels-onecol.tpl.php by hus-->