The warning reads: Undefined index: comment in /var/www/extensions/SecurePoll/includes/pages/VoterEligibilityPage.php on line 787 which is referring to this line in the code:

$that->saveList( $property, $formData['names'], $formData['comment'] );

The form element comment seems to be defined further up in the code, but it is actually not shown for any of the eligibility lists. Code should be modified to make the comment textbox show.