try changing the folowing code:
<?php
// WA eCart Redirect
if ($tenacitas->redirStr != "") {
header("Location: ".$tenacitas->redirStr);
}
?>
to:
<?php
// WA eCart Redirect
if ($tenacitas->redirStr != "") {
session_commit();
header("Location: ".$tenacitas->redirStr);
}
?>