Permission denied when 'show_in_menu' is set for Custom Post Type

Hi,

I have managed to group some Custom Post Types under a Menu Page which I created by using the

add_menu_page()

function and they show up perfectly. I can view all posts created for each Custom Post type and I can edit them all.

The problem is that I cannot create new posts for the Custom Post Types! I have googled and several others have had the same experience.

What am I missing?

The only things I have added to my

register_post_type()

functions to group them is 'show_ui' => true, 'show_in_menu' => 'my_group_page',.

I created the group page like this:

function my_group(){
	add_menu_page('My Group Page', 'My Group Page', 'publish_group_types', 'my_group_page', '', 'dashicons-format-aside', 72);
}

add_action('admin_menu', 'my_group');

Does anyone know What else I am missing?