在joomla 2.5.7中找到“受限访问”

I am new to php and joomla.I have a comoponent in joomla 1.5 and I am converting it to latest version but dont know why am I getting this error "Restricted access"?

  <?php
        // no direct access
     defined( '_VALID_MOS' ) or die( 'Restricted access' );

    require_once( $mainframe->getPath( 'toolbar_html' ) );

     $category=$_REQUEST['category'];

     switch ($category) {
    case 'flash':
        TOOLBAR_homepage::_FLASH();
        break;

    case 'contentbox':
        TOOLBAR_homepage::_CONTENTBOX();
        break;
    /*  
    case 'social':
        TOOLBAR_homepage::_SOCIAL();
        break;
    */
    case 'options':
        TOOLBAR_homepage::_OPTIONS();
        break;

    case 'metatags':
        TOOLBAR_homepage::_METATAGS();
        break;

    default:
        TOOLBAR_homepage::_DEFAULT();
        break;
}
?>

Thanks in advance.

Change _VAILD_MOS to _JEXEC :

defined('_JEXEC') or die( 'Restricted access' );