Can't add friends by upload contact files now?

This afternoon,I readed 500_a_Day_facebook_fan_pages and find the way of adding friends by uploading contact file.But after I uploaded contacted files produced by acute_email_ids_production_engine_9.0,facebook always told me that all of the contacts are on facebook,but I can't add them,there is just no such options.I just can send invitations to those who are not on facebook.What's the probleM?