Entity UI not seems to work for bundled types

In mymodule_entity_info_alter, I put this :

function mymodule_entity_info_alter(&$entity_info) {
  $tribe_types = entity_load('tribe_type');
  foreach ($tribe_types as $type_name => $type) {
    $entity_info['tribe']['bundles'][$type_name] = array(
      'label' => $type->name,
      'admin' => array(
        'path' => 'admin/structure/tribe-types/manage/%tribe_type',
        'real path' => 'admin/structure/tribe-types/manage/' . str_replace('_', '-', $type->name),
        'bundle argument' => 4,
        'access arguments' => array('administer tribe types'),
      ),
    );
  }
}

But when I try to acces to 'tribe/add' (the path defined in mymodule_entity_info at 'admin ui'), there is a fatal error :

Fatal error: Cannot access empty property in /.../www/modules/field/field.attach.inc on line 198

And in field.attach.inc, I think it's fields attachements which doesn't work correctly. I look in this file, and I ask, in my tribe_form (the form for editing/adding), how $entity (or $tribe in my case) is initialized ?
Because it seems that in field.attach.inc, field_attach_form try to access to a property of $tribe object for each field associated. So entity.module make this or it's to me to create an empty property for each field for adding a 'tribe' entity ?
It's my tribe_form code :

function tribe_form($form, &$form_state, $tribe, $op = 'edit') {
  global $user;
  if ($op == 'clone') {
    $tribe->label .= ' (cloned)';
    $tribe->name .= '_clone';
  }
  if ($op == 'add') {
    $tribe->created = time();
    $tribe->updated = time();
    $tribe->uid = $user->uid;
		if($tribe->type == '')
		$tribe_type = arg(2);	
  }
  if ($op == 'edit') {
    $tribe->updated = time();
  }

  if($op == 'add' || $op == 'create') {
    $form['label'] = array(
      '#title' => t('Description'),
      '#type' => 'textfield',
      '#default_value' => $tribe->label,
      '#description' => t('The human-readable name of this tribe.'),
      '#required' => TRUE,
    );
    // Machine-readable type name.
    $form['name'] = array(
      '#type' => 'machine_name',
      '#default_value' => isset($tribe->name) ? $tribe->name : '',
      '#disabled' => entity_has_status('tribe', $tribe, ENTITY_IN_CODE),
      '#machine_name' => array(
        'exists' => 'tribe_load',
        'source' => array('label'),
      ),
      '#description' => t('A unique machine-readable name for this tribe. It must only contain lowercase letters, numbers, and underscores.'),
    );
  }
  else {
    $form['description'] = array(
      '#title' => t('Description'),
      '#type' => 'item',
      '#markup' => 'Nom : "'.$tribe->label.'" ('.$tribe->name.')',
    );
    $form['label'] = array(
      '#type' => 'hidden',
      '#default_value' => $tribe->label,
    );
    // Machine-readable type name.
    $form['name'] = array(
      '#type' => 'hidden',
      '#default_value' => $tribe->name,
    );
  }
  // values.
  $form['created'] = array(
    '#type' => 'hidden',
    '#default_value' => isset($tribe->created) ? $tribe->created : time(),
  );
  $form['updated'] = array(
    '#type' => 'hidden',
    '#default_value' => isset($tribe->updated) ? $tribe->updated : time(),
  );
  $form['type'] = array(
    '#type' => 'hidden',
    '#default_value' => isset($tribe->type) ? $tribe->type : '',
  );
  $form['uid'] = array(
    '#type' => 'hidden',
    '#default_value' => isset($tribe->uid) ? $tribe->uid : 0,
  );

  field_attach_form('tribe', $tribe, $form, $form_state);

  $form['actions'] = array('#type' => 'actions');
  $form['actions']['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Save tribe'),
    '#weight' => 40,
  );

  if (!entity_has_status('tribe', $tribe, ENTITY_IN_CODE) && $op != 'add') {
    $form['actions']['delete'] = array(
      '#type' => 'submit',
      '#value' => t('Delete tribe'),
      '#weight' => 45,
      '#limit_validation_errors' => array(),
      '#submit' => array('tribe_form_submit_delete')
    );
  }
  return $form;
}

And I've changed the fieldable property of 'tribe_type' entity to FALSE, and it works.

And I have a second question : the error happens when I try to access 'tribe/add', or because 'tribe' entity type has bundles, so doesn't 'tribe/add' is a path for displaying different bundles (like 'node/add' displays different node-types), for me the tribe-type entities ?

Sorry for english once again, it's difficult to explain this more or less complex problem...

It's ok, the UI seems to work in fact, just the 'tribe/add' page doesn't work, it will be useful if this page load links for different bundles.
So the error for bundled entity type is for adding, the path '/add' try to load the edit form, but the bundle field is not set so the error is triggered.

I've discover another bug I think, the path returned by 'uri callback', so for my 'tribe' entity type, 'tribe_uri()', is well-set in the page '/tribe' (for the links for each tribe), but when I access this path, the page isn't found.
So there is a problem for uri callback.