problem with wp_dashboard_cached_rss_widget

/**
 * Add widget to the dashboard
 * @since 0.1
 */
function dnxsc_feed_display() {
    wp_add_dashboard_widget('dnxsc-dashboard-feed', __('Slackware Security Advisories', 'dnxsc'), 'dnxsc_feed');
}
add_action('wp_dashboard_setup', 'dnxsc_feed_display' );

/**
 * check the feed for a chached version
 * @since 0.1
 */
function dnxsc_feed() {
    $url = array(
        'http://dev.slackware.it/rss/slackware-security.xml'
    );
    wp_dashboard_cached_rss_widget( 'dnxsc-dashboard-feed', dnxsc_feed_output(), $url );
}

function dnxsc_feed_output() {
    $url = 'http://dev.slackware.it/rss/slackware-security.xml';
    $rss = fetch_feed($url);

    if ( is_wp_error($rss) ) {
        if ( is_admin() || current_user_can('manage_options') ) {
            echo '<p>';
            printf(__('<strong>RSS Error</strong>: %s'), $rss->get_error_message());
            echo '</p>';
        }
        return;
    }

    if ( ! $rss->get_item_quantity() ) {
        echo '<p>' . __('Weird, but there are no items in the Slackware Security Announcements Feed') . "</p>\n";
        $rss->__destruct();
        unset($rss);
        return;
    }

    if ( ! isset($items) )
        $items = 10;
?>
<div class="dnxsc_container">
    <p class="dnxsc_list_desc">
        <img class="dnxsc_tux alignright" src="<?php echo plugins_url() . '/danixland-slackcheck/inc/images/tux512x594.png'; ?>" alt="got slack?" />
        <?php _e("These are the last 10 entries in the Slackware Security Announcements Mailing List.", "dnxsc"); ?>
    </p>
    <div class="clear">
        <ul>

<?php

    foreach ( $rss->get_items(0, $items) as $item ) {
        $title = $item->get_title();

        $content_data = explode('+--------------------------+', $item->get_description());
        $content = html_entity_decode( $content_data[1], ENT_QUOTES, get_option('blog_charset') );

        $links_data = $item->get_item_tags(SIMPLEPIE_NAMESPACE_RSS_20, link);
        $link = esc_url($links_data[0]['child']['']['p'][0]['data']);
?>
            <li>
                <p class="dnxsc_item_link"><a href="<?php echo $link; ?>" title="<?php echo $title; ?>" target="_blank"><?php echo $title; ?></a></p>
                <p class="dnxsc_item_desc"><?php echo $content; ?></p>
            </li>
<?php } // endforeach ?>

        </ul>
    </div>
    <br class="clear" />
    <div class="dnxsc_buttons">
        <p class="dnxsc_list_desc"><?php _e("For more info about the List please check out the links below.", "dnxsc"); ?></p>
        <div class="alignright"><a class="button-primary" href="http://www.slackware.com/security/"><?php _e('View all SSA', 'dnxsc'); ?></a></div>
        <div class="alignright" style="width:7px">&nbsp;</div>
        <div class="alignleft"><a class="button" href="mailto:majordomo@slackware.com?subject=list%20subscription&body=subscribe%20slackware-security"><?php _e('Subscribe to SSA', 'dnxsc'); ?></a></div>
        <br class="clear" />
    </div>

</div><!-- end .dnxsc_container -->

<?php
    $rss->__destruct();
    unset($rss);
} // end dnxsc_feed_output()