There is no way to disable the anti-dragon shields around the harbour or High Hall.
For the barrier in the channel south of the harbour, there are four ballistas that you need to destroy (surrounded by a blue lightning kind of effect), one of which may be just inside the barrier, IIRC (Fire Sphere can take care of that, or I think it is still within Fire Breath range).
I got the game as soon as it was available, which, around here, was several days after the official North American release date (Jan 5th), and have been following the forum since forever.
