When I upload it to a website, it will play if I place the URL of the generated HTML page in the address bar.
When I place it in a frame or iframe it can't find the page. I've not had this issue with html pages with flash players in them.
Also your browser should support iframe element. To troubleshoot this issue you can test out your webpage in a different browser or go to http://html5test.com/ and check if all the necessary options are supported by your browser.