Strange Database Error Today...Not Sure Why.

[RedTurtle]

I had a random vBulletin database error today on my forum. It seems to have occurred when someone was using the search feature.

Here is the error:

Database error in vBulletin 4.2.1:

Invalid SQL:

                        SELECT post.*,userfield.*, usertextfield.*, user.*, IF(displaygroupid=0, user.usergroupid, displaygroupid) AS displaygroupid,avatar.avatarpath, NOT ISNULL(customavatar.userid) AS hascustomavatar,
                                                customavatar.dateline AS avatardateline, customavatar.width AS width, customavatar.height AS height,
                                                customavatar.height_thumb AS height_thumb, customavatar.width_thumb AS width_thumb, customavatar.filedata_thumb
                        FROM post AS post
                                LEFT JOIN user AS user ON (user.userid = post.userid)
LEFT JOIN userfield AS userfield ON (user.userid = userfield.userid)
LEFT JOIN usertextfield AS usertextfield ON (user.userid = usertextfield.userid)
LEFT JOIN avatar AS avatar ON (avatar.avatarid = user.avatarid)
LEFT JOIN customavatar AS customavatar ON (customavatar.userid = post.userid)
                        WHERE post.postid IN (.);

MySQL Error   : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 10
Error Number  : 1064
Request Date  : Wednesday, November 6th 2013 @ 05:45:50 AM
Error Date    : Wednesday, November 6th 2013 @ 05:45:50 AM
Script        : http://mydomain.com/search.php?searchid=103436&pp=&page=16
Referrer      : http://mydomain.com/search.php?searchid=103436&pp=&page=16


IP Address    : 175.110.xxx.xxx
Username      : Unregistered
Classname     : vB_Database
MySQL Version :

Anyone have any idea what could be causing this? Have not made any modifications to the site recently.

Thank you.