TYPO3.Fluid

Hello...I just try to learn Fluid, but when I want to save some values following error appears:

#1251730702: The value must be of type "Tx_Sffluid_Domain_Model_Customer", but was of type "array".

edit.html:
<p class="bodytext">Editieren Sie den Kunden:</p>
<f:form method="post" action="update" name="customer" object="{customer}">
<label for="firstname">Vorname</label><br />
<f:form.textbox property="firstname" /><br />
<label for="lastname">Nachname</label><br />
<f:form.textbox property="lastname" /><br />
<f:form.submit class="submit" value="Submit"/>
</f:form>

CustomerController.php:
class Tx_Sffluid_Controller_CustomerController extends Tx_Extbase_MVC_Controller_ActionController {
protected $customerRepository;

public function initializeAction() {
   $this->customerRepository= t3lib_div::makeInstance('Tx_Sffluid_Domain_Repository_CustomerRepository');
  }
  public function indexAction() {
   $this->view->assign('zahl', 12);
   $this->view->assign('customers', $this->customerRepository->findAll());
  }
  public function editAction(Tx_Sffluid_Domain_Model_Customer $customer) {
   $this->view->assign('customer', $customer);
  }
  public function updateAction(Tx_Sffluid_Domain_Model_Customer $customer) {
   $this->customerRepository->update($customer);
   $this->flashMessages->add('Der Kunde wurde aktualisiert.');
   $this->redirect('index');
  }
 }

I can't find an error. The code is nearly the same as in blog_example. What's wrong here?!

Stefan Frömken

Fluid: 1.0.2
TYPO3: 4.3.1