Show previous and next image thumbnails

[mattrude]

When looking at an Image, display the next image thumbnail, and previous image thumbnail.

Example: http://mattrude.com/2011/08/summer-at-the-cabin/img_3231/

[mattrude]

The needed code, taken from the Milly theme:

<div class="image-navigation">
    <div class="floatright">
        <?php $attachments = array_values(get_children( array('post_parent' => $post->post_parent, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order ID') ));
        foreach ( $attachments as $k => $attachment )
            if ( $attachment->ID == $post->ID )
        break;
    $attachments = array_values(get_children( array('post_parent' => $post->post_parent, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order ID') ));

    $next_url =  isset($attachments[$k+1]) ? get_permalink($attachments[$k+1]->ID) : get_permalink($attachments[0]->ID);
    $previous_url =  isset($attachments[$k-1]) ? get_permalink($attachments[$k-1]->ID) : get_permalink($attachments[0]->ID);
    if ( wp_get_attachment_image( $post->ID+1 ) != null ) { ?>
    <p class="attachment">
        <?php _e('Next Image', 'milly') ?><br />
        <a href="<?php echo $next_url; ?>"><?php echo wp_get_attachment_image( $post->ID+1, 'thumbnail' ); ?></a>
    </p>
    <?php }

    if ( wp_get_attachment_image( $post->ID-1 ) != null ) { ?>
    <p class="attachment">
        <?php _e('Previous Image', 'milly') ?><br />
        <a href="<?php echo $previous_url; ?>"><?php echo wp_get_attachment_image( $post->ID-1, 'thumbnail' ); ?></a>
    </p>
    <?php } ?>
    <div class="floatright">
        <?php edit_post_link('Edit Image'); ?>
    </div>
</div>

[mattrude]

Function is already in the theme, but it's broken.