Unregistered connection type

[raffaelecolleo]

Hi all,
I am getting this error
Warning: Unregistered connection type ''. in /home/demolms/public_html/wp-content/plugins/posts-to-posts/vendor/scribu/lib-posts-to-posts/list-renderer.php on line 8

This is my connection registration
function p2p_courses_to_vocabulary(){
p2p_register_connection_type( array(
'title' => 'Vocabulary',
'name' => 'vocabulary',
'from' => 'courses',
'to' => 'post',
'reciprocal' => true,
'admin_box' => array(
'show' => 'any',
'context' => 'side'
)
) );
}
add_action( 'p2p_init', 'p2p_courses_to_vocabulary' );

Any Ideas???