FacebookService.SendNotification not working for me

Jun 26, 2007 at 11:35 PM
I am trying to send an invitation to my friends to use my application. I have the following:

private const string fbml = @"<fb:req-choice url='http://apps.facebook.com/darkcanijo/&canvas=1' label='Add TestWidget' ></fb:req-choice>";

friends = _fbService.GetFriends();
_fbService.SendNotification(fbml, friends0.UserId, true);

When I make the call the function returns "".

Can anyone offer some help?