We attempt to develop a fluctuation theory of diblock copolymer melts, which would include short-range fluctuations. The one-loop correction has been found to have an ultraviolet divergence, which is shown to be architecture-dependent. The correlation function S(q) is obtained within the Hartree approach by solving the integral equation. However the solution cannot be related to experiments, because of the architecture-dependence of the divergence. We conclude that construction of the fluctuation theory with the use of the RPA-derived Hamiltonian is impossible. (C) 2003 American Institute of Physics.