Its well known in the composer world that composers will borrow from others or their previous works when making movie themes.
Anyway, background info here. My mom said to watch the Spiderwick Chronicles because it was pretty good for a fantasy film. I figured I might as well, and sat there, watching every moment and seeing how the music fit. At one part of the film there was a very beautiful piano theme where the old lady was speaking and I thought, "Man I know this theme....I bet James Horner wrote the score!" Sure enough on the back of the dvd case, composer was James Horner. Would have been march harder to discern if he didn't blatantly put "Casper's Theme" at a key point in the film!!!

: Practically note for note it was there. The score as a whole was different, but still, Casper should be able to keep his own theme for himself.
