public function _toHtml()
    {
        $html = parent::_toHtml();
        if (!$html && !Mage::getStoreConfigFlag('dev/template/allow_symlink')) {
            $url = $this->getUrl('adminhtml/system_config/edit', array('section' => 'dev')) . '#dev_template';
            $html = $this->__('Warning: You installed Aoe_Scheduler using symlinks (e.g. via modman), but forgot to allow symlinks for template files! Please go to <a href="%s">System > Configuration > Advanced > Developer > Template Settings</a> and set "Allow Symlinks" to "yes"', $url);
        }
        return $html;
    }