At this point I would recommend going back to PayPal and recreate the add to cart button. You can do that as often as you need to. Then just reinstall it on your page. Preview it and see if it then works. If it does; republish. No biggy...it will just overwrite the page that isn't working.

I've got to go clean house and yard work, so don't think I bailed out on you! I'll check back occassionally! There are others that are much more experienced than I who will probably jump in to help also! Talk later!