to be able to add Universal Email to the page, it must be a dynamic PHP page. The one you should use is the "photoform.php" page.
The error you are getting is because the action of the form is set to go to the photoform.html page, change the forms action to go to photoform.php instead:
A local testing server can be helpful for development, but no 100% necessary, you could use the remote server for testing as well.
if you wish to set up a local testing server, you can use Wamp for windows or Mamp for Macintosh, they are fairly easy to set up:
The Dreamweaver Simulations tab of the Learning resources page:
Has tutorials for configuring your Dreamweaver Site for dynamic web development.