Continuity mistake: When Robin and Spike walk back into Paula's front room and discover her laying dead in front of the TV, Paula's position is now different than just a minute earlier when Robin herself had discovered her before dropping the popcorn bowl.
Continuity mistake: Towards the end of the film, Spike tells Robin he had learned, that in order to stop Mr. Grubeck's astral body from killing, they have to kill the physical body first. But at the very end of the film, Spike, who had been run down just five minutes earlier on his bike and killed by the astral-projected Mr. Grubeck driving a semi, shows up in astral form to push the real Mr. Grubeck over the mountain, in turn killing him. This obviously contradicts the entire theory.