error in Package config

I have one error using the first example of manual about of Config Package error: call to a member function on a non-object in phparray.php line 212 function _getParentString(&$obj) {

       $string = '';
       if (!$obj->isRoot()) {
           if (!$obj->parent->isRoot()) { //IT IS THE LINE 212
               $string = "['".$obj->name."']";
           } else {
               if (empty($this->options['name'])) {
                   $string .= '$'.$obj->name;
               } else {
                   $string .= '$'.$this->options['name']."['".$obj->name."']";
               }
           }
           $string = $this->_getParentString($obj->parent).$string;
           $count = $obj->parent->countChildren(null, $obj->name);
           if ($count > 1) {
               $string .= '['.$obj->getItemPosition().']';
           }
       }
       return $string;

} // end func _getParentString help me. thank you. Paz y Bien Dios les bendiga _________________________________________________________________ Charla con tus amigos en línea mediante MSN Messenger: http://messenger.yupimsn.com/