global.php include

[t0ny]

I have a file outside of vb with the following code:

<?php  
//Store current directory
$cwd = getcwd();
echo getcwd().'\n';
//change to forum directory
chdir ('../forum');
echo getcwd() . '\n';

require_once('global.php');
if ($vbulletin->userinfo['userid'])  
{  
    echo 'Welcome ' . $vbulletin->userinfo['username'] . ', you have logged in.';  
}  
else  
{  
    echo 'Not logged in...';  
} 
//return to original directory
chdir ($cwd);
echo getcwd().'\n';
?>

I am getting this error when I use it :

Unable to add cookies, header already sent.

Can anyone help??