Using form_open inside a block crashes everything

[Tomas Sandven]

This is my code. If I remove form_open, the code works.

<? require 'application/views/templates/base.php' ?>

<? startblock('body') ?>

    <?= form_open('auth/login/confirm') ?>
        <table>
            <caption>Login</caption>
            <thead>
                <tr>
                    <th><?= form_label('username', 'Username') ?></th>
                    <th><?= form_label('password', 'Password') ?></th>
                </tr>
            </thead>
            <tbody>
                <tr>
                    <td><?= form_input('username') ?></td>
                    <td><?= form_input('password') ?></td>
                </tr>
            </tbody>
        </table>
    <?= form_close() ?>

<? endblock() ?>

Here's the error message