Problemer men login

Jeg bruger flg. kode i toppen af siden:

<?php
if(!isset($PHP_AUTH_USER)) {
        Header(\"WWW-authenticate: basic realm=\\\"??????\\\"\");
        Header(\"HTTP/1.0 401 Unauthorized\");
        $title=\"Login Instructions\";
       
        exit;
    } else {
        mysql_pconnect(\"localhost\",\"nikolaj\",\"**********\") or die(\"Kan ikke finde SQL serveren\");
        mysql_select_db(\"user\") or die(\"Kan ikke finde databasen!\");
        $user_id=strtolower($PHP_AUTH_USER);
        $password=md5($PHP_AUTH_PW);
        $query = mysql_query(\"select * from users where username=\'$user_id\' and password=\'$password\'\");
        if(!mysql_num_rows($query)) {
            Header(\"WWW-authenticate: basic realm=\\\"????????\\\"\");
            Header(\"HTTP/1.0 401 Unauthorized\");
            $title=\"Login Instructions\";
           
            include \"inc/header.phtml\";
            print\"<br>\";
            print\"<h3><center>Du har ikke adgang til denne side</center></h3>\";
            include \"inc/footer.phtml\";
           
            exit;
        }
       
       
        mysql_free_result($query);
    }

?>

Men jeg for en Internal Server Error i fejl log stå der :
[Sun Sep 02 17:25:26 2001] [error] [client 127.0.0.1] malformed header from script. Bad header=HTTP/1.0 401 Unauthorized: d:/apache/php4/php.exe

Hvad kan der være galt ???