Pagination not working

Here is my code. Currently I am getting a 404 error every time I try to paginate to page two of my blog listing page. I’m stumped. Please help.

if ( get_query_var('paged') ) { $paged = get_query_var('paged'); }
			elseif ( get_query_var('page') ) { $paged = get_query_var('page'); }
			else { $paged = 1; }

			query_posts('posts_per_page=3&paged=' . $paged);
			?>
			<?php echo $query_string; ?>
			<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

				<?php get_template_part( 'content', 'post' ); ?>

			<?php endwhile;?>
			<h3><?php posts_nav_link( $sep, $prelabel, $nextlabel ); ?></h3>