This is usually done to report a validator error, not a validator ...
$element->setErrorMessages(array(Zend_Validate_...::CONSTANT => 'New Message'));
But I often prefer to redefine all element errors to one
$element->setErrorMessages(array('Single Error'));
or, if I need it on a validator, it works ...
$validator->setMessages('string error')
. , . - ?
, , , , .