<? 
    $res = $database->userLatestStatus($u);
    while($row=mysql_fetch_assoc($res)){
       $status=$row['status'];
       echo "$status";
    }
    ?>

This is the code on my page, which is throwing up the following error: Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource....

The database function:

   function userLatestStatus($u)
   {
       $q = "SELECT status FROM ".TBL_STATUS." WHERE userid = '$u' DESC LIMIT 1";
       return mysql_query($q, $this->connection);
   }

Any ideas what the problem is?