Customize webform-fields error messages
Go ahead and download this https://drupal.org/node/1209450 module in zip. there are two zips you can download any one. here is the code can you use now

function modulename_message_alter(&amp;$message) {

    if(isset($message-&gt;messages['error'])){
       foreach($message-&gt;messages['error'] as &amp;$val) {
        if(preg_match('@The entered date must be \w+/\w+/\w+ or \w+.@',$val)){
            $val='This is not correct date';
        }
       }
    }
}