Session error

Hi.. I'm tryin to check if there is a session created with the IP of the username. Since it's a function I specify the IP in the main file and send it as check_ses($uip) but i get and error saying Warning: Cannot send session cache limiter - headers already sent by (output started at Can anyone help me out? This is the function i use : function check_ses($ip) { session_start(); if (session_is_registered($ip)) { echo "this for other pages"; return 1; } else { session_register('$ip'); } }