Facebook Registration plugin async form validation unsafe javascript warning

I'm trying to implement the registration plugin on my application as documented here:

http://developers.facebook.com/docs/plugins/registration/advanced/

I need to perform an async validation to check for the uniqueness of the user login and email address but the request to the server is being blocked as an 'unsafe Javascript' operation (Domains, protocols and ports must match.)

The form is here: https://www.zooniverse.org/signup?form=facebook

If you type any string into the 'login' field the uniqueness check will be blocked by the browser.

Does anyone have any idea w开发者_如何学JAVAhat I'm doing wrong here?

---

Are you sure it wasn't a temporary facebook issue? Or specific browser issue? When I test it, it works in both FF5 and Chrome13. I get no errors in the console, it doesn't show me an error (unless I pick a reserved login like 'XXX'), and returns the following response:

{"attributes_taken":[]}