I don't know much about HTTPReq object, but I do know what you're doing is illegal 
Some basics (sorry if I go backwards too much) : in Object Oriented Programming, you're dealing (most of the time) with objects. Such objects have :
- A way to create them
- Properties, which are values (or other objects) that define them (think of radius property for a Circle object). They can be read/write but sometimes not both.
- Methods, which are functions that either act upon the object (could be
IncreaseRadiuson a circle) or do things that depend on the object and its properties (could beComputeAreaorComputePerimeterif we keep the Circle object example).
Here, you are using the HTTPReq object and you are trying to apply/call methods on it that are the ones belonging to the MSXML2.ServerXMLHTTP ActiveX object of your first script : it just can't work, and the error message you're getting is exactly telling you that : HTTPReq object does not support the open method.
Note that the examples that were given do not call such a method.
If you want to get a better understanding of the objects (and their properties and methods) available to you, you can get a look at the post I put a link below and more specifically to the link to JScript.
Next thing you'll want to look at is the Opus documentation, and more specifically the Reference/Scripting Reference/Scripting Objects part where you will have a description of all the objects Opus added to the ones provided natively by JScript. These objects will (mostly) be related to Opus.
I'll try and see what you have to change in your code to use the HTTPReq properly based on what @errante provided.