I think I'm having the same issue, just re-download Galactic Civilizations II after a year or 2 out, but stardock central refuses my login details, even though it's working on here! Not only that, but if I purposely put in an incorrect password, it recognises that it's the wrong password. With the correct details, it still tells me it failed to log in.
Any ideas what in the world is wrong with it? I can't access the updates without Stardock Central apparently!