启用视图助手时出错

$this->addElement('text','evt_amtpersons', array(
     'description'     =>  '<a id="buyCredit" href="/user/register" target="_blank">Dit is een link</a>',
        'filters'   => array('StringTrim', 'StringToLower'),
        'ViewHelper',
            array('Description', array('escape'=>false, 'tag'=>false)),
        'validators'=> array(
            array('StringLength',true,array(1,128)),
        ),
        'required'  => true,
        'label'     => 'aantal hulpverleners',
    ));