I suggest you read about Cross Origin Resource Sharing:
http://en.wikipedia.org/wiki/Cross-origin_resource_sharing
This is protection in the web browser that intentionally keeps you from calling out to a service on a different host than the originating web page.
The service in question has to support a special Access-Control-Allow-Origin header and specific the hostname(s) that it will allow calls to originate from. Another possible work around is to use a service proxy.