Hi I am facing very strange Issue for this newsletter plugin.
1) If I logged at administrator then everything works fine.
2) If I create custom user role - with all the capabilities including 'manage_options' and If User which assign to that user-role and accessing 'preview.php' which loaded with <iframe></iframe> then It is throwing 500 internal server error
for e.g::
GET http://example.com/wp-content/plugins/newsletter/emails/preview.php?1465233775&_wpnonce=a6ec3ff3d7 500 (Internal Server Error)
In short plugin work as expected for Administrator role, But not for custom user role having same capabilities Administrator have including 'manage_options'.
Same issue When we click on "Proceed to edit" - and it opens http://example.com/wp-content/plugins/newsletter/emails/create.php - also showing Access Denied