SQL error viewing specific thread

[fum1n]

SQL error viewing specific thread

Database error in vBulletin 3.7.3:

Invalid SQL:
SELECT usergroupid FROM user 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, May 19th 2009 @ 02:49:44 AM
Error Date    : Tuesday, May 19th 2009 @ 02:49:44 AM
Script        : http://project-7.net/forum/showthread.php?t=826
Referrer      : http://project-7.net/forum/project-7-pre-sales-questions/
IP Address    : ------------------
Username      : fum1n
Classname     : vB_Database
MySQL Version : 5.0.67-community

How do i fix this? its only on that specific thread.