[RedFoxy]

Ok I fixed it, in the regex you must change _- with -_

Change:

if (preg_match('#attachment.php\?attachmentid=(\d+)#s i', $img_url, $matches) AND preg_match('#class=(\'|"|)([a-z0-9_-\s]+)?\s*previewthumb\s*([a-z0-9_-\s]+)?(\\1)#si', $fullurl))

With:

if (preg_match('#attachment.php\?attachmentid=(\d+)#s i', $img_url, $matches) AND preg_match('#class=(\'|"|)([-_a-z0-9\s]+)?\s*previewthumb\s*([-_a-z0-9\s]+)?(\\1)#si', $fullurl))