Hello.
I have noticed that some images uploaded to the forum are not shown and give the next message:
Invalid Attachment specified. If you followed a valid link, please notify the administrator
I have seen that this happens to some users:
http://www.blenderartists.org/forum/showthread.php?379984-quot-Little-boy-quot-photorealism
And it had also happened to me. When you are writing the message and you upload the image, the image is displayed properly in the preview, but then is not shown when publish the message and you get this Invalid Attachment message.