On the pages with an add to cart button, look for code similar to the following near the doctype tag:
<?php
// WA eCart Redirect
if ($<Your cart Name>->redirStr != "") {
header("Location: ".$<Your cart Name>->redirStr);
}
?>
and change it to:
<?php
// WA eCart Redirect
if ($<Your cart Name>->redirStr != "") {
session_commit();
header("Location: ".$<Your cart Name>->redirStr);
}
?>