see the following thread for details on troubleshooting the headers already sent error message:
showthread.php?t=19285
according to the error, the problem is at line 1 of the index page:
output started at /home/stjohnd/public_html/test_donations/index.php:1
this means either there is output to the page at line 1, or the Unicode BOM Signature is enabled
to clear the carty on checkout success, add the following code after the </html> tag on the checkout success page:
<?php
// Initialize the session.
// If you are using session_name("something"), don't forget it now!
@session_start();
// Unset all of the session variables.
$_SESSION = array();
// If it's desired to kill the session, also delete the session cookie.
// Note: This will destroy the session, and not just the session data!
if (ini_get("session.use_cookies")) {
$params = session_get_cookie_params();
@ setcookie(session_name(), '', time() - 42000,
$params["path"], $params["domain"],
$params["secure"], $params["httponly"]
);
}
// Finally, destroy the session.
@session_destroy();
?>