If you haven't beaten the Elite 4 yet, then it won't budge. After you have, go back to it and it will move and you can follow it.
It will not move until you beat the game.
I beleive that this is what you mean. It's a glitch that was only in place in the japanese games.
In the Japanese versions of Pokémon Black 2 and White 2, if the player begins following N's Zoroark through Victory Road then leaves the area, Zoroark will appear in its initial position and will not move. This prevents the player from meeting N. This bug was fixed in international releases.
This video may help to explan: http://www.youtube.com/watch?v=cZPfeBxQa4g
You have to beat the Pokemon league and follow it I wish I could catch it but I'm sure its N's Pokemon.