Thanks for your help LenK and RVoodoo-
I put the code you suggested in index.php, after “Not Found” error which you accurately predicted, but still it doesn’t show. I moved it around to a few different positions and nothing ever seemed to change as far as the navigation at the bottom of the page.
I don’t understand where the problem is – here’s the bottom part of my index.php which I edited and am using currently:
<?php comments_template(); ?>
<?php endwhile; else: ?>
<h2><?php _e('Not Found','lightword'); ?></h2>
<p><?php _e("Sorry, but you are looking for something that isn't here.","lightword"); ?></p>
<?php if(function_exists('wp_pagenavi')) { wp_pagenavi(); } ?>
<?php endif; ?>
<div class="newer_older">
<span class="newer"> <?php previous_posts_link(__('« Newer Entries','lightword')) ?></span>
<span class="older"> <?php next_posts_link(__('Older Entries »','lightword')) ?></span>
</div>
</div>
<?php get_sidebar(); ?>
<?php get_footer(); ?>
And my site is https://www.19thstep.com
The page-nav plugin is enabled!
Thanks again, I appreciate it!