I went by the form program online and copied and pasted the html for the thank you page. I changed the email address and subject line. I did not change the 3rd blue line. I uploaded the thank you page and tested it. I received this message:
The requested URL/action.php was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use and ErrorDocument to handle the request.

What did I do wrong? How can I fix this?

Thanks!
Erica