Cannot register the game on steam!

Hi,

i bought galactic civilization on steam and tried to launch it.

When i try to register, there is a window which says, key is already connected to another account. I have no other key, than the key which is supplied by steam. (I did not register with a different e-mail!) My other stardock game Sins of a solar empire is running proberly.

So i cannot play the game. What is wrong?