Database error in creating BBCODE

[marcos_]

Database error in vBulletin 3.6.7:

Invalid SQL:
SELECT userid FROM post where threadid =   AND userid = 50;

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 'AND userid = 50' at line 1
Error Number : 1064
Date         : Tuesday, May 13th 2008 @ 05:51:45 PM
Script       : http://www.********.com/admincp/bbcode.php?do=modify
Referrer     : http://www.********.com/admincp/index.php?do=nav
IP Address   : ---------
Username     : -------
Classname    : -------

I want to make a bb code. i pressed create then this warning shown on the panel.

why? and how to i fix it?

note: vB 3.6.7