Out of memory for backup

[eluser]fs_xyz[/eluser]
Hi there,
I got a problem regarding backup. It used to be fine... Last time I used was about a week ago.
Here is the script I use :

Code:

<?php
class BackupDatabase extends Controller {

    function __construct()
    {
        parent::Controller();
        $this->load->helper('download');
        $this->load->helper('file');        
        $this->load->dbutil();                
    }
    
    function index()
    {
        $now = date("d-m-Y H:i:s");
        $prefs = array(
            'format'      => 'gz',
            'filename'    => 'backup '.$now.'.sql',
            'add_drop'    => TRUE,              
            'add_insert'  => TRUE,        
            'newline'     => "\n"
            );
        $this->dbutil->backup($prefs);
        $backup =& $this->dbutil->backup();

        force_download('backup '.$now.'.gz', $backup);        
    }
    
}
?>

I got this error message :
Fatal error: Out of memory (allocated 24903680) (tried to allocate 18361504 bytes) in ../system/database/DB_utility.php on line 347

I wonder what is happening ? If about php.ini... I'm afraid I don't access for that.
I also tried ini_set(), didn't work.
I use patched CI 1.7.2, and I don't think the patch got anything to do with download process.

Can someone help me ? Sorry for the broken english. Thank you in advance.

PS : Uhh, I just realized, I posted in the wrong section. I'm sorry, can anyone move this to the correct one ?