As far as I know there is only one code for it, but it can be a bit tricky. What you have to do is keep holding the trigger for the code (select, unless you changed the trigger to something different) while you walk through the doorway, all the way until you're inside. What I do is hold Select until I see the stationary inside. Hope that helps!
Hey Agonist, I was searching through your stuff on Pokecheck and I saw that you had two Kyurems from the same Black game. I tried using the rebattle code for Kyurem but it didn't work, you know, the one that rebattles Kyurem plus the musketeers and Reshiram and Zekrom. I was wondering if you used a different rebattle code or the same one (if one at all).