Database Error: Invalid SQL After Installing Various vB.org Modifications

[Wheezy]

I recently downloaded and installed a few vB.org modifications onto my forum, and I have been greeted with this database error when using the "New Posts" link and "Search" box in the navbar.

Database error in vBulletin 3.7.0:

Invalid SQL:

			SELECT post.pagetext AS preview,
				thread.threadid, thread.threadid AS postid, thread.title AS threadtitle, thread.iconid AS threadiconid, thread.dateline, thread.forumid,
				thread.sticky, thread.prefixid, thread.taglist, thread.pollid, thread.open, thread.lastpost AS postdateline, thread.visible,
				thread.hiddencount, thread.deletedcount, thread.attach, thread.postusername, thread.forumid,
				
				replycount, IF(views<=replycount, replycount+1, views) AS views,
				thread.lastpost, thread.lastposter, thread.lastpostid
			,
				deletionlog.userid AS del_userid, deletionlog.username AS del_username, deletionlog.reason AS del_reason,
				user.userid AS postuserid
				, NOT ISNULL(subscribethread.subscribethreadid) AS issubscribed
				
				, attachment.thumbnail_filesize AS thumbsize , MIN(attachment.attachmentid) AS attachmentid 
			FROM thread AS thread
			LEFT JOIN user AS user ON(user.userid = thread.postuserid)

			LEFT JOIN deletionlog AS deletionlog ON(thread.threadid = deletionlog.primaryid AND deletionlog.type = 'thread')
			
			 LEFT JOIN subscribethread AS subscribethread
				ON(subscribethread.threadid = thread.threadid AND subscribethread.userid = 1 AND canview = 1)
			LEFT JOIN post AS post ON(post.postid = thread.firstpostid)
			
			LEFT JOIN attachment as attachment ON(attachment.postid = thread.firstpostid AND (attachment.extension = 'jpg' OR attachment.extension = 'gif' OR attachment.extension = 'png')) 
			WHERE thread.threadid IN
		(529, 134);

MySQL Error   : Mixing of GROUP columns (MIN(),MAX(),COUNT()...) with no GROUP columns is illegal if there is no GROUP BY clause
Error Number  : 1140
Request Date  : Sunday, April 19th 2009 @ 04:52:25 PM
Error Date    : Sunday, April 19th 2009 @ 04:52:26 PM
Script        : http://www.mysite.com/search.php?searchid=1797
Referrer      : http://www.mysite.com/forumdisplay.php?f=56
IP Address    : **.***.**.***
Username      : MyUsername
Classname     : vb_database
MySQL Version : 4.0.27-max-log

I don't know where to start because I have no clue what the problem means! Any advice would be much appreciated.