Yes. As many as one in four people are unhypnotizable; for such individuals, hypnotherapy is unlikely to be effective. Brain imaging studies have revealed differences in patterns of brain connectivity between those who respond to hypnotism and those who do not. Specifically, scans of individuals who can be hypnotized show heightened co-activation between the executive control center in their prefrontal cortex and another part of the prefrontal cortex that flags the importance, or salience, of events.
Others who could conceivably be hypnotized also may not respond to the technique because of deep skepticism of it or resistance to enter a hypnotic state.