I had a look at it and it's easy to fix:
OPEN
warn.php
FIND
PHP Code:
if ($vbulletin->options['warn_auto_ban'] && ($UserData['inferno_warn_level'] + $Warning['amount']) >= $vbulletin->options['warn_max_level'])
REPLACE WITH
PHP Code:
if ($vbulletin->options['warn_auto_ban'] && ($UserData['inferno_warn_level'] + $Warning['amount']) >= $vbulletin->options['warn_max_level'] && $Warning['method'] == 'plus')