When I click edit or create new newsletter I get an 404

When I click edit or create new newsletter I get an 404 error saying the page doe snot exists.

The link is
http://www.payoffratio.com/wp-admin/customize.php?wp_customize=on&theme=&newsletter_id=2&return=admin.php%3Fpage%3Dnewsletters

Any ideas?

Thanks

James