get_current_user_id() returns 0 on extra php site

The following Code has been working fine for over 3 years. Last week, i set up a new Server with The same OS and the same Webserver (Windows Server 2012R2 + IIS 8) and now it Returns NULL…. I have no Idea what could be different between these two Servers…. Maybe any configuration on my Webserver in relation to the Sessions?!

I hope someone could help me…

I use following Code:

require_once(‘../wp-load.php’);
get_currentuserinfo();
global $current_user;
$user_id = $current_user->ID;
echo $user_id;

I know taht i use the Right directory to load my wp-load File.