The problem was that you used
[attachthumb] or [attach]
in your post.
Those are only for images.
If you simply add nothing to your message, you will see your file available as an attached item for download at the bottom of your post.
OR you could do
which is the same (shows a download link) except that you decide where in your post the download link is shown.
I've gone ahead and modified your post for you to show you.