Forum DB Error: cant delelet thread with "keep attachements" unchecked
 

Code:
Database error in vBulletin 4.0.1:

Invalid SQL:

UPDATE post AS p
SET p.attach = (
SELECT COUNT(*)
FROM attachment AS a
WHERE
p.postid = a.contentid
AND
a.contenttypeid = 1
GROUP BY a.contentid
)
WHERE p.postid IN (170787);

MySQL Error : Column 'attach' cannot be null
Error Number : 1048
Request Date : Tuesday, January 19th 2010 @ 10:51:18 AM
Error Date : Tuesday, January 19th 2010 @ 10:51:18 AM
Script : http://[...]/forums/postings.php?do=...&threadid=8472
Referrer : http://[...]/forums/postings.php
IP Address : [...]
Username : [...]
Classname : vB_Database_MySQLi
MySQL Version : 5.1.30
what should I do?

no plugins enabled except vb cms/blog.