My game doesn't work

I hadn't played GalCiv 2 for a couple of months, so when I went back to play it a couple of days ago I was surprised and horrified when it wouldn't start. I decided that a patch might fix this, so I updated the game through Stardock Central and tried to play. The game asked me for my e-mail address and serial number so I input both of them, copying the serial number from my game disc, but it said that the serial number was invalid. I then tried having Stardock e-mail me my serial number so that I could paste it in and avoid any mistakes, but the number was the same and so I got the same result. As far as I know I'm stuck: this isn't a pre-owned game, but I've entered the correct serial number and it still won't let me play. Am I missing something obvious, or am I stuck with the most expensive placemat I've ever bought?

I checked the thread on this problem, but none of the options seem to apply to me. I don't have the American edition, it isn't a collector's edition, I'm using the correct serial number, and it isn't a used or pirate copy.