As well as not being able to open the web page, when I type in my Product & serial no. it says not recognized, but it is shown on my account details!!
vívofit® 2
Serial Number: 431231885
I had the same problem using Firefox on Mac. When I did the same with Safari on Mac, it worked.
Whether that is down to Firefox or one of the add-ons I have installed, I don't know.
Your problem may be completely unrelated, but thought I would mention it in case you want to try it with a different browser.