The module add a call to an ajax page that creates a javascript error

The javascript to allow the forum to be collapsed has a call to an ajax page which is creating an error because of a call to an incorrect function.

function advanced_form_ajax($op, $container_id = NULL) {
  global $base_url;
  $base_url = str_replace('.', '_', $base_url);
  switch($op) {
    case 'load':
      if(!isset($_COOKIE[$base_url.'_advanced_forum'])) {
        //Set defaults in the cookie.
        $defaults = variable_get('advanced_forum_collapse_defaults', array());
        setcookie($base_url.'_advanced_forum[tids]', serialize($initial_state), time()+60*60*24*30, '/');
      }
      else {
        $initial_state = unserialize($_COOKIE[$base_url.'_advanced_forum']['tids']);
      }
      print drupal_to_js(array('tids' => $initial_state));// orginal call was to drupal_json
      break;
    case 'toggle':
      if(!$container_id)
        exit;
      if(!isset($_COOKIE[$base_url.'_advanced_forum'])) {
        $defaults = variable_get('advanced_forum_collapse_defaults', array());
      }
      else {
        $initial_state = unserialize($_COOKIE[$base_url.'_advanced_forum']['tids']);
      }
      $initial_state[$container_id] = 1 - $initial_state[$container_id];
      setcookie($base_url.'_advanced_forum[tids]', serialize($initial_state), time()+60*60*24*30, '/');
      break;
  }
}

The drupal_json call is not available in drupal-5.x but the drupal_to_js is, which seems to have eliminated the javascript error, and allow normal operation.