>I find it rather intersting that the Vatican is trying to get people to boycott this movie.
> ...

I was wondering about this myself. I haven't seen the movie, nor the book, and I am not very interested. But from what I heard, it seems that (according to the story) someone uncovers a secret plot by the Vatican, to cover the "real story", namely, that Jesus survived, and had descendants. Now, if I understood this plot part correctly, I see three potential problems for the Church.

The claim that they are behind some sort of cover-up.

The idea that Jesus survived. He was supposed to have died for our sins.

And, finally, the idea that He had children - it seems that this goes against the ideas of some people about "purity".

Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)