[installatione moduli] - Cannot modify header information

[stratboy]

Ciao, ho fatto un modulo semi-vuoto, solo per test. Sia installandolo che disinstallandolo (in admin/positions), continuo ad avere sto errore:

 

Warning: Cannot modify header information - headers already sent by (output started at [...] /prestashop/modules/customshippingrates/customshippingrates.php:93) in [...] /prestashop/classes/Tools.php on line 141

 

La classe l'ho praticamente quasi svuotata ma ancora ho quel warning. La classe è la seguente:

 

<?php
/*
* 2013 Luca Reghellin
*/

//controlla l'esistenza della costante (una qualunque).
//Serve solo per prevenire che questo file venga direttamente caricato da hackers
if (!defined('_PS_VERSION_')) exit;

class CustomShippingRates extends Module{
 public function __construct(){
   $this->name = 'customshippingrates';
   $this->tab = 'shipping_logistics';
   $this->version = '1.0';
   $this->author = 'Luca Reghellin';
   $this->need_instance = 0;
   $this->dependencies = array();

   parent::__construct();

   $this->displayName = $this->l('Custom shipping rates');
   $this->description = $this->l('Shipping rates based on items volumes.');

   $this->confirmUninstall = $this->l('Are you sure you want to uninstall?');

 //questo è solo un esempio, non è necessario
if (!Configuration::get('CUSTOMSHIPPINGRATES_NAME')) $this->warning = $this->l('No name provided');
 }//END CONSTRUCT
public function install(){
 Configuration::updateValue('CUSTOMSHIPPINGRATES_NAME', 'Custom shipping rates');

   return parent::install() &&
   //$this->registerHook('actionCartSave') &&
   $this->registerHook('displayHome');
}
public function uninstall(){
  if (!parent::uninstall() ||
  !Configuration::deleteByName('CUSTOMSHIPPINGRATES_NAME'))
  return false;
  return true;
}
public function hookActionCartSave(){

}

public function hookDisplayHome(){
}//end display top
}//END CLASS

?>

 

 

Qualcuno sa perché mi esce quel messaggio?