Thanks for your reply.
I changed:
add_action( 'init', 'course_register_meta_boxes' );
function course_register_meta_boxes( $meta_boxes ){
add_filter( 'rwmb_meta_boxes', 'course_register_meta_boxes' );
to:
add_action( 'rwmb_meta_boxes', 'course_register_meta_boxes' );
function course_register_meta_boxes( $meta_boxes ){
add_filter( 'rwmb_meta_boxes', 'course_register_meta_boxes' );
and converted the calls to the new style, but still not outputting anything.
Anything else I need to check?