Zero user sql error

[rincefire]

Hi.
after upgrade to 3.7 from 3.6.8 i get the same error over and over on login and logout screens.
funny thing, on the test installation with the very same files i get no such error.

Database error in vBulletin 3.7.0:
Invalid SQL:

		SELECT 
		userfield.*, usertextfield.*, user.*, UNIX_TIMESTAMP(passworddate) AS passworddate,
			IF(displaygroupid=0, user.usergroupid, displaygroupid) AS displaygroupid
			
		FROM prefix_user AS user
		LEFT JOIN prefix_userfield AS userfield ON (user.userid = userfield.userid)
		LEFT JOIN prefix_usertextfield AS usertextfield ON (usertextfield.userid = user.userid) 
		
		WHERE user.userid = 0;

MySQL Error   : 
Error Number  : 
Request Date  : Thursday, July 17th 2008 @ 11:33:59 AM
Error Date    : Thursday, July 17th 2008 @ 11:33:59 AM
Script        : http://*my site*/login.php?do=logout&logouthash=fce854a65381166ab43f7e64884e11572755c690
Referrer      : http://*my site*/forum/
IP Address    : ***
Username      : root
Classname     : vB_Database_MySQLi
MySQL Version :

The problem is, there is no actual error, as this query is valid and returns a row consisting of nulls, but somehow i, and the whole userbase get this error report.
I can`t possibly think of a reason to search for user 0, as there shouldn`t be one.
Reinstalling from scratch is not an option, unfortunately, as the database is quite large and importing it would take loads of time and work.
Thanks in advance