Facebook FBML issue - req-choice required as part of request-form content?

When I try to send invitations from my site, I am getting开发者_开发问答 this error, "req-choice required as part of request-form content". What does it mean?

These are the details I gave when I created application:

App. Name : mysitename
ConnectURL: http://www.mysite.com/

Below is the code I am using. Am I missing something?

<fb:serverfbml style="background-color:#F7F7F7;">
    <script type="text/fbml">
        <fb:fbml>
            <fb:request-form
                  action='http://www.mysite.com/confirm.php'
                  method='POST'
                  invite='true'
                  type='mysite'
                  content='Come and join us. Visit us at http://www.mysite.com/'
                  <fb:req-choice url='http://www.mysite.com/' label='Join'/>
                  <fb:multi-friend-selector
                  showborder='false'
                  actiontext='Invite your friends to join'
                  rows='4'
                />
            </fb:request-form>
        </fb:fbml>
    </script>
</fb:serverfbml>

I believe your tag attributes are a bit out of order. The content attribute of an fb:request-form is a string that should contain the fb:request-choice tag. The best way to do this is to use double-quotes around the content attribute value, and single quotes for everything inside that. You need to re-organize your code like this:

<fb:request-form
    action="http://www.mysite.com/confirm.php"
    method="POST"
    invite="true"
    type="mysite"
    content="Come and join us. Visit us at http://www.mysite.com/
        <fb:req-choice url='http://www.mysite.com/' label='Join'/>
    "
>
    <fb:multi-friend-selector
        showborder="false"
        actiontext="Invite your friends to join"
        rows="4"
    />
</fb:request-form> 

Note how the fb:req-choice tag is actually inside the content attribute string.