Thread Problem, vB Error

[natecoupons]

I've been getting weird messages in my inbox, which is saying I have errors. I get generally 4-5 an hour, and it doesn't seem to be affecting the site.

Here is the error:

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 : Sunday, November 29th 2009 @ 06:18:49 PM
Error Date : Sunday, November 29th 2009 @ 06:18:50 PM
Script : http://www.weusecoupons.com/upload/s...ad.php?t=37430
Referrer : http://www.google.com/search?hl=en&c...&aq=f&oq=&aqi=
IP Address : 67.142.161.23
Username : Unregistered
Classname : vB_Database
MySQL Version :

What is weird is that this thread exists and is perfectly fine. It's located here:
http://www.weusecoupons.com/upload/w...-rr-deals.html

My question is why is the thread id number off??

Google is sending people to thread id 37430, BUT it's on the site as 37382. I was wondering if anyone had any reason why this was happening.