Maybe his service throws an error when there's an unknown parameter, however that's a workaround anyhow. The problem is that MSXML.XmlHttpRequest has poor cache control, to correct this you can use a different object which has no cache at all.
On line 11/12 change 'MSXML2.XMLHTTP.6.0' to 'MSXML2.SERVERXMLHTTP.6.0'; I can't speak to what other functional changes this may cause.
