Most of the "horror stories" simply involve the basic challenge of trying to write a 300-page description of a movie you haven't seen yet, which is probably in production at the same time you're writing the book, and dealing with various last-minutes changes. ("We shot a new ending, so we're faxing you the revised script pages. Can you rewrite the last chapter by Monday?")
On the fun side: Kevin Grievoux of the UNDERWORLD movies once let me pick his brains over the phone regarding the backstory he had invented for his own character, which I worked into one of my novelizations. And there are worse ways to spend a day than hanging out on the Warner Bros. lot checking out the costumes and props for MAN OF STEEL . . .