Getting a Weird Error

[natecoupons]

Database error in vBulletin 3.7.2:

Invalid SQL:
SELECT COUNT(postid) AS posts FROM post WHERE userid =;

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 1
Error Number : 1064
Request Date : Tuesday, November 24th 2009 @ 07:28:00 PM
Error Date : Tuesday, November 24th 2009 @ 07:28:00 PM
Script : http://www.weusecoupons.com/upload/showthread.php?p=6
Referrer : http://www.weusecoupons.com/upload/walgreens/
IP Address : 200.205.57.1
Username : MaxxMe
Classname : vB_Database
MySQL Version : 5.0.85-community

I'm getting these all over the place, and I haven't done anything recently. Any thoughts?

I had a user private message me with an issue earlier. But it seems to be affecting random threads