HTTP Authentication problem

Question

http authentication giving some errors, portion of oracle authentication working fine. Please help me.
Error is:
Warning: Cannot modify header information - headers already sent by (output started at d:\inetpub\wwwroot\vars.php:5) in
d:\inetpub\wwwroot\login.php on line 4
Warning: Cannot modify header information - headers already sent by (output started at d:\inetpub\wwwroot\vars.php:5) in
d:\inetpub\wwwroot\login.php on line 5
My softwares are:
PHP: 4.3.4
OS: Windows 2000 Server          
Oracle 8i client;
Code is:
-------------------- login.php ------------------------
<?include"vars.php";?>
<?php
function authenticate() {
header('WWW-Authenticate: Basic realm="My Realm"');
header('HTTP/1.0 401 Unauthorized');
exit();
if(!isset($PHP_AUTH_USER)) {
authenticate();
echo "Authorization Failed.";
exit;
}else {
$dbconn=ocilogon($dbUser,$dbPass,$dbName);
$parsed=ociparse($dbconn,"select username from users where username='$PHP_AUTH_USER' and password='$PHP_AUTH_PW'");
ociexecute($parsed);
$nrows = ocifetchstatement($parsed, $results);
if ($nrows == 0) {
authenticate();
else {
for ($i = 0; $i < $nrows; $i++)
setcookie("USERID", $results["USERNAME"][$i]);
$UserID = $results["USERNAME"][$i];
?>
------------------- vars.php ----------------------
<?php
$dbUser="scott";
$dbPass="tiger";
$dbName="db";
?>

Answer 1

Is there any extra whitespace outside the <?php ?> tags?
It might be treated as HTML text and cause the default
header to be sent before authenticate() is called.
There is something similar mentioned in this thread:
Re: fetching blob results in "Call to a member function on a non-object "
-- CJ