Continuity mistake: In the scene where Kat is being introduced to her new classmates, Casper is seen tying the students' shoelaces together. This includes the snobby blonde sitting in front. But when the camera pans out, her feet are clearly too far apart for this, not like how they showed them while being tied.
Continuity mistake: When Dr. Harvey sees his dead wife, Amelia, for the first time as a ghost, he talks to her half way up the staircase in the manor while the party is going on. The camera changes angles a few times from the side of their heads, to Amelia's view of Dr. Harvey. In each different camera angle, his hair changes place, from the side of his head, it slips down in front of his face.
Continuity mistake: When the kids take a vote for having the Halloween dance at Whipstaf, the blonde girl is standing in front of the class as all the kids raise their hands and the bell rings. The shot then goes to the bell and then back to the kids sitting in their chairs. The blonde girl is sitting in her seat when a few seconds ago she was standing up. Also when all the kids get up to leave and trip, we see that none of their shoes are actually tied even though Casper tied them a few moments earlier.