Disable comments by default on new pages and custom post types, while still giving you the ability to individually set them on a page or post basis.
The second possible issue is that you are duplicating a post or page. This plugin only works when you are on a new post/page screen, while plugins that duplicate posts, duplicate the post first and then take you to an edit screen. Unfortunately, there is no way to get around this issue, so if you plan on using a duplication plugin, then you will just have to remember to disable your comments.
Depending on your theme or plugin that created custom post type "X", that post type may not have comments set up. If this is the case, this plugin cannot help you and you will have to talk to your theme/plugin author.
Many themes will include text to show that comments are not enabled on a post. To remove it, you would need to talk to your theme author.
First, you must make sure you can see the Discussion admin box. Enable this by clicking on the 'Screen Options' tab at the top right and then checking the discussion checkbox. Below the post/page editor, there will be a new admin box allowing you to specifically enable or disable comments and trackbacks for that page or post.
Of course, although it is highly recommended that you backup your blog's database prior to completing this step. Go to the 'No Page Comment' settings page and scroll to the bottom of the page. There is an area that will allow you to either enable or disable both comments and trackbacks for any post type you have installed on your blog.
Donations are always accepted, but I am also looking for help from others who want to make this plugin better. Please fork the plugin on Github and feel free to report any issues. Also, I am looking for people who are interested in translating No Page Comment into other languages. Please contact me me if you are interested.