The European release date has been pushed back because of BUGS and STABILITY PROBLEMS. German gamer's magagzine "Gamestar" couldn't really test "Clear Sky", because it was almost unplayable. The AI is more or less retarded, and the game testers were beamed to places they couldn't get out anymore by the "tour guide" (or whatever it'll be called in the English version).
So, the serial key is more or less a lame excuse for all of this. They need to finish the game, get rid of the bugs and release it in a playable form.