thx for the reply, well in fact I'm just facing a bug...I checked the walkthroughs on wiki before posted. and they just said:
"Back to Main hall, now go to the middle entrance. You find yourself in a labyrinth, but don't worry, you can't get lost here. Explore both sides so you get all chests and find yourself facing Karin the Dragoon, the 3rd Strongest member! (Nope, all seems fine to me). Beat her take the Queen Key, go to the top left Corner and look at the Statue, use the Crowbar. Follow the small path. A total of 8 chests in this room: Mid-Potion, Blue Ether, Contact Poison, Throwing Axe (x3), Scroll of Lesser Quickness, Resurrection Potion, Wolfslayer Ring, and Scroll of Force Barrage)."
I find this secret room, face to karin, try to talk her with the 4keys but the battle don't start .