The droid that gives you the mission for Karagga's Palace is inside the instance, right behind the shuttle you board at the beginning of the Op. (In the Hutta Operations Hangar). You have to be in a group to access this one. You can only take these missions one time.
To be more precise: what he means is that you can only have the quest FOR the Eternity Vault once. It awards you with some Tionese-commendations. But you can run the operation itself as many times as you possibly can by just walking to the door of the operation and entering.