vBulletin Database Error!

[twigman1200]

I keep getting the following sent to my email:

Invalid SQL:
SHOW COLUMNS FROM user LIKE 'username';

MySQL Error : Can't create/write to file '/tmp/#sql_b3902_0.MYI' (Errcode: 28)
Error Number : 1
Request Date : Sunday, February 26th 2012 @ 12:29:55 PM
Error Date : Sunday, February 26th 2012 @ 12:29:55 PM
Script : http://www.halo4news.net/forum/regis...p?do=addmember
Referrer : http://www.halo4news.net/forum/register.php
IP Address : 173.242.124.212
Username : vutkaws723
Classname : vB_Database
MySQL Version :


Any suggestions how I can fix this?