Cannot create custom post types with a specific name

Question

I am creating custom post types using this code

function create_custom_post_type() {
    register_post_type('courses',
        array(
            'labels' => array(
                'name' => __('Courses'),
                'singular_name' => __('Course')
            ),
            'public' => true,
            'has_archive' => true,
            'rewrite' => array('slug' => 'courses'),
            'supports' => array('title', 'editor', 'thumbnail', 'excerpt'),
            'taxonomies' => array('category')
        )
    );
}
add_action('init', 'create_custom_post_type');

This code successfully works and shows and the archive pages shows as well but the posts give a 404 error, If i name the custom post types anything else like Lessons then it works I have done everything like cleared the rewrite rules, saved the permalink settings again after creating a post but it does not work Can anyone help Thanks,