I have 4.0.18, but I do not think there is that much difference. I would think it would work. Do me a favor and go to my site and go through the purchase process... don't fill in credit card info, just see if the click box and submit works for you if you check it. This will tell us if it is implemntation of the script or if it is your browser or computer.
Here is the store:
http://www.dinnerandamurder.com/store/catalog/index.html