gistfile1.php

<?php
/**
 * Determines if there are problems with the registration data submitted
 *
 */
function pw_rcp_validate_user_fields_on_register( $posted ) {

	if ( is_user_logged_in() ) {
	   return;
    	}

	if( empty( $posted['rcp_profession'] ) ) {
		rcp_errors()->add( 'invalid_profession', __( 'Please enter your profession', 'rcp' ), 'register' );
	}

	if( empty( $posted['rcp_location'] ) ) {
		rcp_errors()->add( 'invalid_location', __( 'Please enter your location', 'rcp' ), 'register' );
	}

}
add_action( 'rcp_form_errors', 'pw_rcp_validate_user_fields_on_register', 10 );