When the novel The Nanny Diaries became a surprise hit last spring, its authors, former nannies Emma McLaughlin and Nicola Kraus, were catapulted from haute servitude on the Upper East Side to the best-seller lists, the talk-show circuit and a Miramax movie deal. But has their triumph only opened up the doors of discontent for the pair?" The authors are now on their thirdliterary agent, andsources familiar with their business dealings saidMs. Kraus and Ms. McLaughlin are unhappy about the details of the movie deal they signed before their book hit it big.