WordPress blog integration not working: Error Establishing a Database Connection

I am in the process of integrating wordpress with opencart.

I have succesfully installed wordpress at mydomain.com/wp , it works fine and I can access everything as needed.

I have this, placed just before the start of my opencart header tag on a specific page.

<?php 
/* Short and sweet */
define('WP_USE_THEMES', false);
require('wp/wp-blog-header.php');
?>

and I am receiving an “Error Establishing a Database Connection” error, clearly it is finding wp-blog-header, wordpress at mydomain.com/wp is also working fine and thus connecting to the DB which is why I am confused as to what the problem is. I have a feeling it could be related to this specifically the FILE in wp-config but I am not sure?

if ( !defined('ABSPATH') )
    define('ABSPATH', dirname(__FILE__) . '/');