I wanted to warn people about an error within WordPress that affects all use of custom posts/taxonomies when adding them to the menu.
Just to clarify, this is not an error within Custom Press, but WordPress itself.
If you have created some custom post types/taxonomies, and then add those to the menu by selecting them, but you then remove the custom post types/taxonomies from the system, but not the menu, this will cause your menus page to break, and you will have nothing more than a white screen with a small dot in the top left corner.
So, if you have added post types/taxonomies to your menu in this way, you should remove them from the menu before removing them from Custom Press itself.
One way around this, is to create a custom link within the menus area, linking to the location of the post type/taxonomy.