Probleme Undefined index: url100x100

Bonjour,
Je suis actuellement le tuto cake php jour 2 et j'ai un problème d'url...
erreur :

Notice (8): Undefined index: url100x100 [APP\Controller\MediasController.php, line 62]

MediaController :

<?php
class MediasController extends AppController{

    public $components = array('Img');

    public function beforeFilter(){
        parent::beforeFilter();
        $this->layout = 'modal';
    }

    function admin_index($post_id){
        if($this->request->is('post')){
            $data = $this->request->data['Media'];
            if(isset($data['url'])){
                $this->redirect(array('action'=>'show','?class=&alt=&src='.urlencode($data['url']
                    )));
            }
            $dir = IMAGES.date('Y');
            if(!file_exists($dir))
                mkdir($dir,0777);
            $dir .= DS.date('m');
            if(!file_exists($dir))
                mkdir($dir,0777);
            $f = explode('.',$data['file']['name']);
            $ext = '.'.end($f);
            $filename = Inflector::slug(implode('.',array_slice($f,0,-1)),'-');
            //Sauvegarde en BDD
            $success = $this->Media->save(array(
                'name' => $data['name'],
                'url'  => date('Y').'/'.date('m').'/'.$filename.$ext,
                'post_id'=> $post_id
            ));
            if($success){
                move_uploaded_file($data['file']['tmp_name'], $dir.DS.$filename.$ext);
                foreach(Configure::read('Media.formats') as $k=>$v){
                    $prefix = $k;
                    $size = explode('x',$v);
                    $this->Img->crop($dir.DS.$filename.$ext,$dir.DS.$filename.'_'.$prefix.'.jpg',$size[0],$size[1]);
                }
            }else{
                $this->Session->setFlash("L'image n'est pas au bon format","notif",array('type'=>'error'));
            }
        }
        $d = array();
        $d['medias'] = $this->Media->find('all',array(
            'conditions' => array('post_id' => $post_id)
        ));
        $d['formats'] = Configure::read('Media.formats');
        $this->set($d);
    }
    function admin_show($id=null,$format = ''){
        $d = array();
        if($this->request->is('post')){
            $this->set($this->request->data['Media']);
            $this->layout = false;
            $this->render('tinymce');
            return;
        }
        if($id){
            $this->Media->id = $id;
            $media = current($this->Media->read());
            $d['src'] = Router::url('/img/'.$media['url'.$format]);
            $d['alt'] = $media['name'];
            $d['class'] = 'alignLeft';
        }else{
            $d = $this->request->query;
            $d['src'] = urldecode($d['scr']);

        }
        $this->set($d);
    }   

    function admin_delete($id){
        $this->Media->id = $id;
        $file = $this->Media->field('url');
        unlink(IMAGES.DS.$file);
        $f = explode('.',$file);
        $ext = '.'.end($f);
        $file = implode('.',array_slice($f,0,-1));
        foreach(glob(IMAGES.DS.$file.'_*.jpg') as $v){
            unlink($v);
        }
        $this->Media->delete($id);
        $this->Session->setFlash("L'image a bien été supprimée","notif");
        $this->redirect($this->referer());
    }
}

Merci d'avance :)