I seem to be having the similar problem. I first played darkspore when it arrived in the stores and then left it until now when i decided I would like to play it some more. However Upon entering my login details I receive the message saying that I needed to enter my retail key. I found it in my box and entered it only to find it said it was already in use. Now as for some reason It appears I have two e-mails linking to a single account which I find awfully strange I checked both to see if it was the other one which was active. But no, neither of them are. I also followed to Support as suggested but there is nothing on there about how to solve this and no direct contact, from what I can see, to a living human being. I honestly expected more from EA's support services....
But I have tried entering my key in
www.darkspore.com/productI also seemed to be able to redeem on origin but when I play it from Origin it stills prompts me to add my key
I also know I have the game, in real life as I am sitting with the box, CD and Code next to me now.
And I bought it from a legal retailer, AKA GAME
Any other help would be greatly appreciated... Or if nothing I suppose I will need to buy a new key.....