Loading Wordpress environment into PHP file working on localhost but not on server

I have the following issue. I want to load the Wordpress environment into an external php file. All my work is currently on a localhost and my php code is as follows:

<?php
require("../../wp-blog-header.php");

$admin = do_shortcode("[su_user field='user_email']");

if ($admin === "admin@email.com") {

    // Do stuff here

}

else {

    echo "<h1>Forbidden.</h1>";

}

This works perfectly fine in my localhost, so I figured that when I upload the file to the server it must work too, given that the file is stored in the same directory as it is locally, hence ../../wp-blog-header.php. Sadly, this does not work. When I echo $admin; the following error appears:

User: user ID is incorrect

I tried using the native Wordpress functions without using the shortcode like this:

<?php global $user_email;
      get_currentuserinfo();

      echo $user_email;
?>

This does not work either. Is there a more efficient way to load the Wordpress environment into an external php file? Any suggestions on what is happening here? It does not necessarily have to be an e-mail, it could be the user id as well, which I tried and gives me 0.

via Chebli Mohamed