The aim is to show a form which will update the div on the page with the result
When you submit the form, the request is sent to the server and you obtain a HTTP Error: 405 Method Not Allowed
.
It looks like it comes from the configuration of your server. http://www.checkupdown.com/status/E405.html
Edit: as your code works for your example in the facy.html page I think it doesn't really comes from the server. The difference between the two examples are the action of the form.
Did you try to call your thank you page "thanks.php" and modify the action of your form accordingly. I suppose that your server might not allow POST request on an HTML page.