getting userid on custom page

[squishi]

On a custom page that is called periodically with ajax, I would like to check the userid of the user. (I want to compare it with a variable to show a ban button in my chat application).

So this is what I have:

PHP Code:

    chdir('../../forum');
        require_once('./global.php');
        echo "vbuserinfo: ".$vbulletin->userinfo['userid'];
        die(); 


But vbulletin-userinfo['userid'] is zero ("vbuserinfo: 0").
I am logged in at the forum and global.php is found. I don't understand why it's not working.