Hello and welcome to BigBlueBall!
Since the router is obviously the cause of the problem, I would say that you do not have the right ports open.
Read
http://support.dlink.com/faq/view.asp?prod_id=1428 for a list of the ports that need to be opened.
However, I know for a fact that getting Super Webcam to work behind a router is near impossible as I have tried it myself. I have tried opening ports..tried DMZ, it just didn't want to work. I just gave up. Hopefully you have a better experience with it.