Its probably stolen by those people who pirate. You might want to contact sals@stardock.com (someone please verify) and ask them for help.
That doesn't make sense since pirates tend to not need CD-keys, or if they do, used ones but then CRACK the game. I would know as I actually did pirate Sins. But eariler this year I did buy it, the CE version actually.
But yea get in contact with sals@stardock.com or something. Probably just a double of a CD-Key or someting.