I'm trying to call wp_title() from /includes/languages/english/My_Template/meta_tags.php
and it gives me a "PHP Fatal error: Call to undefined function wp_title()"

Code:
define('META_TAG_TITLE_BLOG', wp_title() . '');

I have

Code:
require('../wordpress/wp-blog-header.php')
(which *should* be including all the functions I need) working correctly because my blog pages display.

Any thoughts on why it isn't working? Does the 'require' need to be placed higher up in the code?

Blog page found here: http://nelsontactical.com/blog

Thanks!