Database Error

[Xplorer4x4]

PHP Code:

SELECT * FROM user FORCE INDEX (lastactivity)
WHERE lastactivity > 1173426936 ORDER BY username;

MySQL Error : Key 'lastactivity' doesn't exist in table 'user'
Error Number : 1176
Date : Saturday, March 10th 2007 @ 07:55:36 AM
Script : /index.php
Referrer : /index.php
IP Address : 
Username : Xplorer4x4
Classname : vb_database 


I have deleted all my hacks and now I have this error. I deleted all my hacks due to one of them decided to enable debug mode and disable most admin cp functions.