Fejlbesked omkring header

Hejsa,

Har dette script der bruges til bruger-login:
    <?
    // login.php - performs validation
    // authenticate using form variables
    $status = authenticate($f_user, $f_pass);
    // if  user/pass combination is correct
    if ($status == 1)
    {
    // initiate a session
    session_start();
    // register some session variables
    session_register("SESSION");// including the username
    session_register("SESSION_UNAME");
    $SESSION_UNAME = $f_user;
    // redirect to protected page
    header("Location: /upload.php");
    exit();
    }
    else
    // user/pass check failed
    {
    // redirect to error page
    header("Location: /error.php?e=$status");
    exit();
    }
    // authenticate username/password against a database
    // returns: 0 if username and password is incorrect
    //          1 if username and password are correct
    function authenticate($f_user, $f_pass)
    {
    // configuration variables
    // normally these should be sourced from an external file
    // for example: include("dbconfig.php");
    // variables explicitly set here for illustrative purposes
    $db_host = "xxx";
    $db_user = "xxx";
    $db_pass = "xxx";
    $db_name = "xxx";
    // check login and password
    // connect and execute query
    $connection = mysql_connect($db_host, $db_user, $db_pass) or die
    ("Unable to connect!");
    $query = "SELECT id from users WHERE username = '$f_user' AND password = '$f_pass'";
    mysql_select_db($db_name);
    $result = mysql_query($query, $connection) or die ("Error in query: $query. " . mysql_error());
   
    // if row exists -> user/pass combination is correct
    if (mysql_num_rows($result) == 1){
        return 1;
    }
    // user/pass combination is wrong
    else{
        return 0;
   
    }
    }
    ?>

Men hver gang jeg kører det får jeg flg. fejl:

Warning: Cannot modify header information - headers already sent by (output started at xxx\logintest.php:1) in xxx\logintest.php on line 22

Hjælp:-)