Folks... you've got my head spinning in circles -- this is a default installation so far... and the contents of those two files I posted are exactly as they came "out of the box!"

Mark... no variables ever appear in the URL once https://www.sandbox.paypal.com/us/cgi-bin/webscr is hit, until it gets back to http://www.eranaturalbeauty.com/PayPal/PDTHandler.aspx. However, the transaction is indeed happening - I can see it in the PayPal sandbox, and the sandbox emails seem to be being sent!

In checking my PayPal profile to be sure all is setup properly, I found that the Instant Payment Notification Preferences are ON and pointed at: http://www.eranaturalbeauty.com/PayPal/IPNHandler.aspx -- but when I plug that into the browser, I get the following error:

Object reference not set to an instance of an object.

System.NullReferenceException: Object reference not set to an instance of an object.
   at IPNHandler.Page_Load(Object sender, EventArgs e) in d:\ultimaweb\bruce@ztechsystems.net\eranaturalbeauty.com\wwwroot\PayPal\IPNHandler.aspx.cs:line 19
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Under Website Payment Preferences, I have Auto Return On, and the return URL as: http://www.eranaturalbeauty.com/PayPal/PDTHandler.aspx (this provides the exact same error message as noted is my earlier message)  -- also, Payment Data Transfer is On, and the Identity Token is what I'm using as my PDT ID. Encrypted Website Payments is Off, PayPal Account Optional is On and Contact Telephone Number is Off.

Am I being really obtuse here, or is the PayPal Standard implementation in CSK really confusing???