note 29970 rejected from function.session-start by rioter

When I try to use the session data on another page, i get this warning: Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/coldatc/public_html/haze/dbd3/index.php:16) in /home/coldatc/public_html/haze/dbd3/index.php on line 104 The script works, as I can access the hidden features, but I get the ugly warning. I have saved this page as login.php, and it will happily set the session data and display the hidden content: <?php session_start(); if ($_POST['username'] == 'haze' and $_POST['password'] == 'foobar') { $_SESSION['username'] = "haze";} ?> <?php if (!$_SESSION['username']): ?> <form method="post" action="login.php"> <input type="text" name="username"> <input type="password" name="password"> <input type="submit" value="go"> <?php else: ?> you are logged in as <?php echo $username; ?>. <br> <a href="index.php">go back</a> &middot; <a href="post.php">post news</a> &middot; <a href="logout.php">log out</a> <?php endif; ?> But it's when I come to request the data on the other page that i get the error: <?php session_start(); ?> <?php if (!$_SESSION['username']): ?> <a href="handlelogin.php">Log In</a> <?php else: ?> you are logged in as <?php echo $username; ?>. <br> <a href="index.php">go back</a> &middot; <a href="post.php">post news</a> &middot; <a href="logout.php">log out</a> <?php endif; ?> What's wrong? I can't see anything wrong, and I followed it according to the documentation on the session_start(); function. :S