NIS for Mac: activation problem

My NIS for Mac expires today. First I tried to renew my subscription, but had no success following the links and kept getting product not found- which was odd as I entered the correct exisiting version of NIS. I then decided to purchase NIS 5 online. Whatever I do, and please have patience as I'm not the most technically minded, I cannot get the product to activate. At no point have I been prompted for the product key. The only prompt, and it has been intermitant, has been for the subscription key- which I do not have. From my Norton account I can see the product key and serial number, but entering these in place of the subscription key does not work. My Norton account keeps prompting me to download the product again as it detects it as not being installed. My Norton account flags the product as not being activated. I've downloaded the software several times, even after uninstalling the original version of NIS. If I open the Anti-virus window, it shows the remaining time as unknown.

 

How do I activate the product? Where do I get a subscription key from? 

 

I'm running a MacBook Pro with OS X 10.6.8