AJAX Extensions 2.0 not working on IIS6

I am deploying an ASP.NET app to a Win2003 Server.  This application uses ASP.NET AJAX Extensions 2.0.  The application runs just fine in my dev environment (Vista), but in the production environment the AJAX does not seem to be functioning.  

As a very simple test, I created a page with one updatepanel.  Inside the updatepanel is a button and a text box.  On clicking the button, the textbox is updated with the datetime.  Outside of the updatepanel is another text box which gets loaded with the datetime on page load only.  In the dev environment, the behavior is as I expected - meaning the text box OUTSIDE of the update panel loads only once and the text box INSIDE of the updatepanel loads on each button click.  When I run this page in the production environment, both text boxes are updated on each button click, meaning that the full page is being loaded every time, rather then just the contents of the update panel.

I am not receiving any errors - even javascript errors (yes I have enabled javascript errors in the browser).  I also did restart IIS after installing the extensions AND verify that the System.Web.Extensions and System.Web.Extensions.Design dlls are in the GAC.

I have also changed the Publish parameters of the application a number of times (I think Ive tried all the checkbox configurations) and it still doesnt work.  I have also tried the page with the ScriptManager both inside the page and inside the masterpage and that didnt make any difference.

Any ideas here?

Thanks.