"include" in php3 and php4

[storm]

I am including file, with part of code that performs authorization, in the beginning of files that need authorization.

Module with authorization:
<?
if(!isset($PHP_AUTH_USER)) {
Header("WWW-Authenticate: Basic realm=\"..\"");
Header("HTTP/1.0 401 Unauthorized");
exit;
} else {
checking login and pass...
if ($auth=="ok") {
?>

And file where it included
<?php
include("auth.php3");
code...
code...
code...
}
} else {
Header("WWW-Authenticate: Basic realm=\"..\"");
Header("HTTP/1.0 401 Unauthorized");
exit;
}
?>

Everything worked well with php3. When I installed php4 at once appeared troubles.

Seems that php4 doesn't parse included code.
Why can it be?

[Anon]

Mayby you call a php3 file, and you have make your server to php4, then php3 don´t work... rename auth.php3 to auth.php4

[storm]

No, it is something else.
It is in the cause of the difference in work of include in php3 and php4. But what is this difference?