wp_get_attachment_image isn't returning thumbnail

I’m trying to get the thumbnail of attachments in my script, but no matter what I do, the result from wp_get_attachment_image() returns the full-sized image.

I’m calling this by:
echo wp_get_attachment_image ($render->ID, "thumbnail");
Where $render is an attachment with these details:

stdClass::__set_state(array(
   'ID' => 564,
   'post_author' => '2',
   'post_date' => '2012-02-23 03:34:25',
   'post_date_gmt' => '2012-02-23 03:34:25',
   'post_content' => '',
   'post_title' => '3D render image',
   'post_excerpt' => '',
   'post_status' => 'inherit',
   'comment_status' => 'closed',
   'ping_status' => 'closed',
   'post_password' => '',
   'post_name' => '3d-render-image-7',
   'to_ping' => '',
   'pinged' => '',
   'post_modified' => '2012-02-23 03:34:25',
   'post_modified_gmt' => '2012-02-23 03:34:25',
   'post_content_filtered' => '',
   'post_parent' => 0,
   'guid' => '',
   'menu_order' => 0,
   'post_type' => 'attachment',
   'post_mime_type' => 'image/jpeg',
   'comment_count' => '0',
   'ancestors' =>
  array (
  ),
   'filter' => 'raw',
))

I’ve also checked and all of the resized images exist and are able to be seen.

The only thing that I cna think of is that I create these attachments using the wp_insert_attachment() function but I though that was what should be used for inserting attachments???

Am I doing something wrong, or is there some other reason that I can’t get the thumbnail image?