add_action vs do_action

Hi supporter,
Before I ask how to can add captcha to my site, and I do it, but have problem.
When CP2 call do_action( 'coursepress_before_signup_validation' );
You don't pass 2 params via it, and when I do add_action( 'coursepress_before_signup_validation' ) $form_message_class , $form_message
, I assign 2params but it not effect to signup validate. Why and how can i do it?
Thank you very much.