Thank you for the fast reply
It works, but now I get this message (frontend and admin side):
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/metiersd/public_html/wp-content/plugins/polylangfix.php:1) in /home/metiersd/public_html/wp-content/plugins/wordpress-simple-paypal-shopping-cart/wp_shopping_cart.php on line 22
Weird!
Is there a conflict with my wordpress-simple-paypal-shopping-cart plugin?