[jasonmerchant]

hmm... well I'm not really sure what is wrong, can you test this:

$thumbsforums = array(210);
$displaythumbs = false;
if (in_array($forumid, $thumbsforums)) {
	$displaythumbs = true;
	$hook_query_fields = "";
	$hook_query_joins = "";
	$hook_query_where = "";
}

If this test is successfull it should display "no thumbnail" images on all threads.

If it still failed then run this test:

$thumbsforums = array(210);
$displaythumbs = false;
if (in_array($forumid, $thumbsforums)) {
	$hook_query_fields .= ", attachment.thumbnail_filesize AS thumbsize , MIN(attachment.attachmentid) AS attachmentid ";
	$hook_query_joins .= "LEFT JOIN " . TABLE_PREFIX . "attachment as attachment ON(attachment.postid = thread.firstpostid) ";
	$hook_query_where .= "GROUP BY thread.threadid ";
}

If this test is successfull it will display your threads normally without thumbnails.

Let me know what your results were.