Thanks, I tried that but it didn't help. I think I have solved the problem, but not in a way that I like:(
In DW, I dragged one of the pages that was not working, into my root directory. DW updated the links and then I uploaded it to my site. It worked perfectly. It added the item to the cart, calculated tax and shipping and all seems well.
So what does this mean? Do all the pages with e-cart buttons have to be in the root directory - or - Do all the pages with e-cart buttons have to be in the same directory of the Shopping Cart (which currently is in my root directory)? or is it something else???