Next Post Links refers to Not Found page

Hello,
I’m writing a custom category template file.
I have like 20 categories, and like 30 posts a category, so my website is getting pretty slow. I’m trying to solve this with a next_post_link(); but it isn’t working. When i click on the next_page_link(); its refers to Not Found Page.

This is how I query my post:

<?php if ( get_query_var('paged') ) {
                                      $paged = get_query_var('paged');
                                    } else if ( get_query_var('page') ) {
                                      $paged = get_query_var('page');
                                    } else {
                                      $paged = 1;
                                    }
                            $args= array(
                                'cat' => $id,
                                'posts_per_page' => 10,
                                'paged' => $paged
                            );
                            query_posts($args); ?>

$id is the category that I fill in with something like this :

<?php if (is_category('7')) : ?>
                    <?php $id = 7 ; ?>
 <?php endif; ?>

Thanks in advance!