Can't hide fields in user registration form at new menu path
Follow Drupal's standards and change your hook_menu:

/**
 * Implements hook_menu().
 */
function MY_MODULE_menu() {
  $items['admin/author/create'] = array(
    'title' =&gt; t('Author'),
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('MY_MODULE_author_form'),
    'type' =&gt; MENU_CALLBACK,
    'access callback' =&gt; TRUE,
  );

  return $items;
}