Ajax

Estou a tentar pôr a funcionar o ajax mas não estou a conseguir.

No controller tenho :

class PostsController extends AppController {

 var $name = "Posts";
 var $helpers = array('Html','Ajax','Javascript');
 var $components = array( 'RequestHandler' );

 function index() {
 $this->set('posts', $this->Post->find('all'));
 }
 function deleteaj($id) {

 $this->Session->setFlash('passou');

 }

a view index contendo a lista de posts dentro do div a actualizar e o link ajax

<?php echo $ajax->div('postsdiv'); ?>

<table>
 <tr>
 <th>Id</th>
 <th>Title</th>
 <th>Actions</th>
 <th>Created</th>
 </tr>

 <!-- Here's where we loop through our $posts array, printing out post info -->

 <?php foreach ($posts as $post): ?>
 <tr>
 <td><?php echo $post['Post']['id']; ?></td>
 <td>
 <?php echo $html->link($post['Post']['title'], array('action' => 'view', 'id' => $post['Post']['id'])); ?>
 </td>
 <td>
 <?php echo $html->link('Delete', array('action' => 'delete', $post['Post']['id']), null, 'Are you sure?') ?>
 <?php echo $html->link('Edit', array('action' => 'edit', $post['Post']['id'])); ?>
 <?php
 echo $ajax->link('Excluir Post',
 array( 'controller' => 'posts', 'action' => 'deleteaj', $post['Post']['id']) ,
 array( 'update' => 'postsdiv' ), 'Você quer mesmo excluir este post?'); ?>

 </td>
 <td><?php echo $post['Post']['created'];
 ?></td>
 </tr>
<?php endforeach; ?>

</table>
 <?php echo $ajax->divEnd('postsdiv'); ?>

o default.ctp tem a inclusão dos js

echo $javascript->link('prototype');
 echo $javascript->link('scriptaculous');

contudo quando clico no link dá o seguinte erro

Notice (8): Undefined variable: javascript [APP\views\layouts\default.ctp, line 33]

Fatal error: Call to a member function link() on a non-object in C:\xampp\htdocs\cakephp\blog\views\layouts\default.ctp on line 33

agora substitui no default ctp por

echo $this->Html->script('prototype');
 echo $this->Html->script('scriptaculous');

mas quando clico no link n faz nada,devia ao menos aparecer o session flash