I have identified the problem occourse here
else if (isset($url_array[$pos+2]) && $url_array[$pos+2]==sefencode(_VM_CHECKOUT)) {
$page = $_GET['page'] = $_REQUEST['page'] = 'checkout.index';
$nonsefstring .= '&page=' . $page;
$ssl_redirect = $_GET['ssl_redirect'] = $_REQUEST['ssl_redirect'] = 1;
$nonsefstring .= '&ssl_redirect=' . $ssl_redirect;
If you comment out a part of this
$ssl_redirect = $_GET['ssl_redirect']; // = $_REQUEST['ssl_redirect'] = 1;
the error is gone, but you will not be directed to the next checkout page anymore
Zappu