Custom post archive and pagination not working

For reasons I won’t go in details into, I have had to create custom posts for our website and now I am having trouble getting the pagination to work on the archives pages for each new post type.

I can have the page display only the first 6 (number I chose) items, but clicking on “Next” leads me to a “Page not found” page.

Here’s how I created the new post types:

function createPostType( $slug, $singularSlug, $name, $singular, $allowComments = true )
{
    register_post_type( $slug,
        array(
            'labels' => array(
                'name' => __( $name ),
                'singular_name' => __( $singular ),
                'menu_name' => __( $slug )
            ),
            'public' => true,
            'has_archive' => true,
            "show_in_menu" => true,
            "show_in_nav_menus" => true,
            "taxonomies" => array("category"),
            "supports" => array( "title", "editor", "author", "thumbnail", "excerpt" )
        )
    );

    if( $allowComments )
        add_post_type_support( $slug, array( 'comments' ) );
}

function createNewPostTypes()
{
    createPostType( "themes", "theme", "Thèmes", "Thème", false );
    createPostType( "articles", "article", "Articles", "Article" );
    createPostType( "galleries", "gallerie", "Galeries", "Galeries" );
    createPostType( "videos", "video", "Vidéos", "Vidéo" );
}

and this is the archive’s template:

<?php
get_header();
?>

    <div id="primary" class="site-content dual-column-layout">
        <div id="content" role="main">
            <?php
            $temp = $wp_query;
            $wp_query = null;
            $wp_query = new WP_Query();
            $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
            $wp_query->query('showposts=6&post_type=articles'.'&paged='.$paged);

            $counter = 0;
            while ($wp_query->have_posts()) : $wp_query->the_post();

                if( $counter == 0 )
                    echo "<div style='clear: both'>";

                echo "<a href='".get_permalink()."'>";
                    echo "<div class=\"post-list-thumbnail\">";
                        generateThumbnail( ThemeThumbnailRenderer );
                    echo "</div>";
                echo "</a>";

                $counter++;
                if( $counter == 2 )
                {
                    echo "</div>";
                    $counter = 0;
                }

                if( ( $wp_query->current_post + 1 ) == ( $wp_query->post_count ) && $counter != 0 )
                    echo "</div>";

            endwhile;
            ?>

            <nav>
                <?php previous_posts_link('« Newer') ?>
                <?php next_posts_link('Older »') ?>
            </nav>

            <?php
            $wp_query = null;
            $wp_query = $temp;  // Reset
            ?>

        </div>
    </div>

<?php
    get_sidebar();
    get_footer();
?>

I have tried the many solutions given by people on this forum, but nothing seems to work. I thought it might have been the URL rewrite problem, but it wasn’t (prior to the current configuration I’m using, I was using the Article Name options for URLs. I now reverted to default). Or at least it does not seem like it is.

I am starting to wonder if a working pagination is something possible for custom post’s archives…