I bought my copy of the game back in March 2010 and only got to register the game now because of the updates. Unfortunately, the Stardock\Account Management\Register Product doesn't accept my serial number.
I tried to follow the link in this thread (https://forums.stardock.com/455712/page/1/) posted by Wizard1956. Most of the stuff written there was quite diffierent - the path since my game is not Steam version; and instead of SDactivate.exe my folder contains Activate.exe.
Nevertheless I executed the command chain in cmd (modified to suit my version) but there was no response, no confirmation, nothing whatsoever. I don't even know if there is supposed to be one.
I'd be really helpful for any kind of help or advice.