$body_classes doesnt print any classes

Hello Drupal Community,

I use Zen to design a project site.

I wanted to use the page.tpl.php file to modify the layout. my general problem now is, that the variable $body_classes does not print out any classes. Only if i am logged in the class "admin menu" (from the module) is shown.

i use the following statement in the body tag of the template:

">

after searching for a while i found out that the $body_classes variable is defined in the template_preprocess_page in /includes/theme.inc. The function has not been modified and the functions for the body_classes look like this:

  $body_classes = array();
  // Add a class that tells us whether we're on the front page or not.
  $body_classes[] = $variables['is_front'] ? 'front' : 'not-front';
  // Add a class that tells us whether the page is viewed by an authenticated user or not.
  $body_classes[] = $variables['logged_in'] ? 'logged-in' : 'not-logged-in';
  // Add arg(0) to make it possible to theme the page depending on the current page
  // type (e.g. node, admin, user, etc.). To avoid illegal characters in the class,
  // we're removing everything disallowed. We are not using 'a-z' as that might leave
  // in certain international characters (e.g. German umlauts).
  $body_classes[] = preg_replace('![^abcdefghijklmnopqrstuvwxyz0-9-_]+!s', '', 'page-'. form_clean_id(drupal_strtolower(arg(0))));
  // If on an individual node page, add the node type.
  if (isset($variables['node']) && $variables['node']->type) {
    $body_classes[] = 'node-type-'. form_clean_id($variables['node']->type);
  }
  // Add information about the number of sidebars.
  if ($variables['layout'] == 'both') {
    $body_classes[] = 'two-sidebars';
  }
  elseif ($variables['layout'] == 'none') {
    $body_classes[] = 'no-sidebars';
  }
  else {
    $body_classes[] = 'one-sidebar sidebar-'. $variables['layout'];
  }
  // Implode with spaces.
  $variables['body_classes'] = implode(' ', $body_classes);

other changes that i make in the page.tpl file are applied correctly. but my body class still looks empty - no matter what i do.

my drupal version is 6.2 and i use zen 2.0

thank you a lot for the support.