Quote - Make SURE you are not logged in as "Guest" when you add P8 to your cart!!!!
Make SURE you log into your account BEFORE YOU ENTER YOUR SERIAL NUMBER!!!!!

I just added the serial after adding the item to the cart, went to check out, it asked me to log in -- and when I was logged in my cart was empty.
It is now not letting me use my P7 Serial number, so I can't buy it until I hear from freaking support.

Same problem here; it let me enter the serial number, and then when I logged in it wouldn't recognise it again. So I shut the machine down, went off for a cup of tea, watched the box for an hour and then tried again, logging in first. Worked fine. Now all I have to do is wait patiently for the postman...