asc-net

in this page http://maximaart.com/newscp/ i have this problem Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/maximasy/public_html/newscp/index.php:1) in /home/maximasy/public_html/newscp/index.php on line 2  my source code is <?php session_start(); include_once("config.php"); include_once("functions.php"); $errorMessage = ''; if (isset($_POST['txtUserId']) && isset($_POST['txtPassword'])) { if ($_POST['txtUserId'] === "$user" && $_POST['txtPassword'] === "$pass") { // the user id and password match, $_SESSION['basic_is_logged_in'] = true; require("main.php"); exit;?>