Including files in Views

[eluser]Unknown[/eluser]
Hi there, I've recently begun setting up a website in Code Igniter and have run into a little problem concerning structure/page setup...

My problem is that in the Views folder I have a sub-folder called "constants" which holds files such as header.php, navigation.php etc. I also have a number of other sub-folders within the Views folder that hold specific Views pages based on sections of the website. So in essence, my Views folder looks like this:

main_view.php
constants
|-header.php
|-footer.php
|-nav.php
about_view.php
some_folder
|-some_file.php

My problem now comes when I try and link a file from the constants folder (i.e. header.php) into the "some_file.php" file.

Code:

<?php require_once('../constants/header.php'); ?>
// This does not work for some reason, and after trying a few other options, I'm stumped!

Any suggestions would be of great help.

Thanks a million in advance,
Matt