Next Post links not working in custom post type shortcode

OK, thank you to ialocin, the $gbquery->max_num_pages solve it!

So there is the clean code :

function livredor_function($atts,$content=""){
    extract(shortcode_atts(array(
        id => ''
    ), $atts));


    ob_start();


    function create_guestbook() {   


        $current_page = (get_query_var('paged')) ? get_query_var('paged') : 0;
        $gbquery = new WP_query("post_type=inliguestbook&showposts=10&paged=" . $current_page);     
        while($gbquery->have_posts()) { $gbquery->the_post();

        ?>
            <div class="guestbook">
                <h3><?php the_title(); ?> <span><?php the_time('j F Y') ?></span></h3>
                <?php the_content(); ?>
            </div>
        <?php
        }   

    ?>
    <div class="pagenav">
         <div class="pagnext"><?php next_posts_link('—›', $gbquery->max_num_pages) ?></div>
        <div class="pagprev"><?php previous_posts_link('‹—', $gbquery->max_num_pages) ?></div>  
    </div>
    <?php
    }   


    wp_reset_query();


    return create_guestbook() . ob_get_clean();

}

add_shortcode('livredor','livredor_function');