ds custom field

Hi,
The "Add custom fields" button is not appearing under "manage fields" on my site. I clicked on all the extras, so I must be missing something. I think the issue is that the conditions in this statement in ds.field_ui.inc are not being met:
if ($entity_type != 'ds_views' && isset($form['#ds_layout']) && user_access('admin_fields') && $view_mode != 'form') {
_ds_field_ui_custom_fields($entity_type, $bundle, $view_mode, $form, $form_state);
}