Problem with Auth

I have created a very simple auth routine that almost copies the example given in the Pear Auth documentation. But despite using the default table structure and making sure I'm entering the correct username/password I still can't access the document. Here is the file I load at the beginning of each document. <? require_once 'Auth/Auth.php'; function loginFunction() {

    /**
     * Change the HTML output so that it fits to your
     * application.
     */
    echo "<form method=\"post\" action=\"" . $_SERVER['PHP_SELF'] . "\">";
    echo "<input type=\"text\" name=\"username\"><br />";
    echo "<input type=\"password\" name=\"password\"><br />";
    echo "<input type=\"submit\">";
    echo "</form>";

} $a = new Auth("DB", $dsn, "loginFunction"); $a->start(); if (!isset($_GET['login'])) { exit(); } ?> The $dsn string is created in the data connection file which is loaded beforehand and is correct. Any suggestions what I'm doing wrong? Leonie