This occurs in the last version of the plugin (2.0.7). It is comparing an emty variable with false, and PHP show notices in development envirionments.
Next version I would change:
wp-content/plugins/mail-subscribe-list/sml.php on line 71
THIS:
if ($_POST[‘sml_subscribe’]) {
FOR THIS:
if (isset($_POST[‘sml_subscribe’]) && $_POST[‘sml_subscribe’]) {
AND
/wp-content/plugins/mail-subscribe-list/index.php on line 62
THIS:
if (!$message) { echo ‘<div style=”padding: 5px;” class=”updated”><p>’.$message.'</p></div>’; }
FOR THIS:
if (!empty($message)) { echo ‘<div style=”padding: 5px;” class=”updated”><p>’.$message.'</p></div>’; }
Miguel.