Hi all!

When I try to include a php file like this:
<?
require "file.php";
?>
I get this error:
Fatal error: Failed opening required file.php'
(include_path='.:/usr/share/php') in /home/test/public_html/file.php on line 1


But when I do it like this:
<?
require "http://mydomain.com/file.php";
?>
it works!

Why is this? I can't figure out why because on some clients it does work both ways.
What is configured wrong here?

Thank you,
Domenico