knightstemplar

Actually that trick had some serious side-effects. This is what Memberpress kindly gave me instead:

function admin_move_meta_box() {
  foreach ( get_post_types() as $post_type ) {
    remove_meta_box( 'mepr_unauthorized_message', $post_type, 'normal' );
    remove_meta_box( 'mepr_unauthorized_message', $post_type, 'side' );
    remove_meta_box( 'mepr_unauthorized_message', $post_type, 'advanced' );
  }
}

add_action( 'admin_head', 'admin_move_meta_box' );

To the OP, ran into a similar situation.
This is what I used, while I try to figure out why other solutions didnt’work.
Add the following to your functions.php file or your snippets plugin:

?>
<style>
#mepr_unauthorized_message.postbox {display:none !important;}
</style>
<?php

The snippet contained in this link was suggested but it didn’t work for me:
https://gist.github.com/DumahX/b199158ba53037a60e1c62f92e2fa01f