I'm adding my frustration too.
I've just installed GalCiv2 Ultimate fresh from Impulse.
It's never been installed on this Win7 32-bit PC before.
I fire up TA and am also told there is no serial number in the registry.
I found this thread searching online, and all the fixes don't work for me due to the same reasons as Zerro0713.
HKEY_CURRENT_USER\Software\Stardock\Settings <- Does not exist to delete.
Deleting the sig.bin file does nothing, it doesn't ask me for details when I fire up the game, I just get the same error when going to the metaverse. I can see it just recreates sig.bin automatically under \Programdata\stardock\twilight\
gc2ul doesn't exist for me either.
I can see my key in Impulse, I guess it's just not in the registry anywhere.
Can I not put it in manually somewhere?