loading user with valid permission fails in DrupalWebTestCase, am I missing something?

The code beneath is in my test class, but when I create a drupal user with the 'user test amfservice' permissions the creation fails (see screenshot of the test).
The 'use test amfservice' is a valid permission in the amfserver module.
Anyone have a clue? Do I need to set it first?

require_once 'SabreAMF/Client.php';

class AmfServerTestCase extends ServicesWebtestCase {
  
  protected $privileged_user = NULL;
  protected $endpoint = NULL;
  protected $client = NULL;
  protected $endpoint_url = NULL;
  

  /**
   * Implementation of setUp().
   */
  public function setUp() {
    parent::setUp ( 'amfserver' );
    // Set up endpoint.
    $this->endpoint = $this->saveAMFEndpoint ();
    $this->endpoint_url = $this->getAbsoluteUrl ( $this->endpoint->path );
    $this->client = new SabreAMF_Client ( $this->endpoint_url );
    $this->client->setEncoding ( 3 );
  }

public function testEndPoint() {
    $page = $this->getEndpoint ( $this->endpoint_url );
    $this->assertContainsText ( $page, 'The amfserver with Zend AMF is installed and working.', 'endpoint call in browser functions normally: ' . substr ( $page, 0, 150 ) . "....", 'amfserver: test' );

    $this->privileged_user = $this->drupalCreateUser(array('administer users', 'access user profiles', 'use test amfservice'));
    $this->drupalLogin($this->privileged_user);

    $page = $this->getEndpoint ( $this->endpoint_url );
    $this->assertContainsText ( $page, 'The amfserver with Zend AMF is installed and working.', 'endpoint call in browser (with logged in user) functions normally: ' . substr ( $page, 0, 150 ) . "....", 'amfserver: test' );
  }