In DKS most of the generators and anti-dragon shields were removed. In Stone's fortress the only one left is by Xanlosch and his creature. You should get a cutscene conversation entering that area (either from the passage, or by flying over the anti-dragon shield and dropping down in human form), followed by a fight. After the fight you should be able to destroy the generator, as described above. You can destroy it earlier, but at least in D2:ED if you take dragon form before defeating Xanlosch he will summon a couple flying opponents.
