The RPX service is supported by LoginRpx.ascx Web part, not the "standard" Login.aspx. You will need to change the RpxFrameUrl property (either interactivelly, via the admin toolbar, or programatically) and set it to the URL assigned to you by Janrain Engage (a new name for the former RPX service) when you register with them.
By default, this URL is set to http://monox.rpxnow.com/openid/embed just to showcase this module - it is our "private" URL and Janrain allows you to define which referring URLs can call it.
In addition to the free registration at Janrain's site, you will need to perform site-specific application creation tasks at each provider sites (Facebook, Google, LinkedIn, whatever). Janrain has a very good documentation and UI ([url=https://rpxnow.com/]https://rpxnow.com/[/url]) that will assist you in this process, please contact us if you need more info.