Rowling says fan's book could endanger other authors - Yahoo! News:
"'Are we, or are we not, the owners of our own work?' said the author of the seven Harry Potter books that have sold about 400 million copies."

NOW we get to the heart of the matter. And I'm afraid I would have to answer to Ms. Rowling, no, you are not the owner of your work once it has been set free into society. Rowling did not sell 400 million copies to herself. Yes, this new book builds on her work. But that's how culture evolves. Copyright was never intended to stifle that. It was intended to allow authors to earn a living from their work, to encourage them to create. It was society's method of funding and rewarding creativity. It has now been perverted to reward corporations and businesses for precisely STIFLING creativity. In the age of zero cost distribution, copyright must be re-considered as a means to promote creativity. I mean, who profits when a book is copyrighted for 75 years after the authors death? Society doesn't. No, J. K. You want to sell your book to the public? Then you need to allow the public to build on your work as it sees fit. There are other ways to "protect" Harry Potter from errors and mis-interpretations. Everyone knows your name on a book is the official word. YOU are the brand not Harry Potter.