How do I call posts with a certain tag?

It’s because when you call query_posts, you’re overwriting the original query with a new one, you have to get the original query and reset the things you want to change.

global $query_string;
$per_page = get_option( 'to_count_archives' );
query_posts( $query_string . '&posts_per_page=" . $per_page );