thanks for developing your plugin!
I've lot of error with WP_DEBUG ON, mainly according to
Notice: has_cap is called with an argument that is depreciated since version 2.0! The use of levels of user extensions and themes is now prohibited. Use roles and capacities in place. in / www / site / wp-includes / functions.php on line 3321
Notice: Undefined index: page in /www/site/wp-content/plugins/wp-responder-email-autoresponder-and-newsletter-plugin/wpresponder.php on line 418
I hope it helps you.