how can i put all eror in same log file

[eluser]Zeeshan Rasool[/eluser]
Hi, guys there is a little prob. Here , i have a code that generates error log file

Code:

$dbRet=$this->db->insert('hfelp_video');
             if (!$dbRet) {
             $errNo   = $this->db->_error_number();
                $errMess = $this->db->_error_message();

            log_message("error", "Problem Inserting to".$errMess." (".$errNo.")");

but, it generates new file daily with current date file name i-e

log-2008-06-30.php , log-2008-07-01.php etc

how can i put all eror in same log file

thnx in adv.