Facebook邀请功能不适用于iframe应用程序

I have registered an iframe application. I want to give invite functionality. I have copied a php code for invite functionality but the invite functionality is not working only blank page is displayed.My code is

<fb:request-form 
    action="<? echo $invite_href; ?>" 
    method="post" 
    type="<? echo $app_name; ?>"
    content="<? echo htmlentities($content,ENT_COMPAT,'UTF-8'); ?>" 
    image="<? echo $app_image; ?>">

    <fb:multi-friend-selector 
            actiontext="Here are your friends who don't have <? echo $app_name; ?> yet. Invite whoever you want -it's free!" 
            exclude_ids="<? echo $friends; ?>" /> 
</fb:request-form> 

But if i change the application from iframe to fbml its working. How can i achieve this using iframe?

Please help

after your code use this:

FB_RequireFeatures(["XFBML"], function() {
    FB.Facebook.init("YOUR API  KEY", "xd_receiver.htm");
});