Thanks for all the quick replies. Still no luck, though.
Removing the standard meta boxes is what the code in my first post was doing (provided it was correct code). I do have to say, though. The taxonomy meta boxes did not appear in the first place, until I used the following code in my functions file.
function kw_add_tags_to_attachments() {
register_taxonomy_for_object_type( 'post_tag', 'attachment' );
}
add_action( 'init' , 'kw_add_tags_to_attachments' );
This is what adds the standard textbox that just takes the slug. But I removed this once I started working with the ACF taxonomy fields.
