Would anyone know why i get this?

[bashy]

Hi peeps

Every now and again i get a db error when someone tries to access a thread
I have had to remove about 10 threads cause of this....

I did think it was sommat to do with GARS but this time the threads is not GARS related

Heres there error....

Database error in vBulletin 3.5.4:

Invalid SQL:
SELECT COUNT(*) AS count FROM user WHERE referrerid =;

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
Date         : Saturday, July 22nd 2006 @ 04:26:22 AM
Script       : http://www.bashys-place.com/forums/showthread.php?t=115&page=2
Referrer     : http://www.bashys-place.com/forums/forumdisplay.php?f=45

Is it due to changing servers and perhaps a different version of SQL?
If so whats the way around this please as i havnt removed this thread yet...?