PHP4 Session Error Message

I have an account by Widexs.nl. Cookies are enabled and cache_limiter=nocachable and safe_mode=on I would like to work with sessions. I've start the session with session_start(); And register the variables with session_register(); Than I get an error message Warning: Cannot send session cookie - headers already sent by (output started at /opt/guide/www.profiteffect.com/HTML/Arnold/addtobasket.php3:5) in /opt/guide/www.profiteffect.com/HTML/Arnold/addtobasket.php3 on line 8 Warning: Cannot send session cache limiter - headers already sent by (output started at /opt/guide/www.profiteffect.com/HTML/Arnold/addtobasket.php3:5) in /opt/guide/www.profiteffect.com/HTML/Arnold/addtobasket.php3 on line 8 Who can helps me? And how must I change the settings on the server. Arnold Geluk