And if you preview the message before posting, I think you have to add the attachment again before you submit the post. Also, if you post the message and the attachment doesn't show up, there doesn't seem to be a way to add an attachment by editing the message. I think you have to start again with a new message. Helpful hint: copy the text of your message before you try to post or preview the message (right click, highlight text and click "copy"). Then if something happens and you lose the message you can right click and paste the text into the new message without having to type it all over again.