Effective potentials for light moduli

We examine recent work on compactifications of string theory with fluxes, where effective potentials for light moduli have been derived after integrating out moduli that are assumed to be heavy at the classical level, and then adding non-perturbative (NP) corrections to the superpotential. We find that this two stage procedure is not valid and that the correct potential has additional terms. Althought this does not affect the conclusion of Kachru et al. (KKLT) that the Kaehler moduli may be stabilized by NP effects, it can affect the detailed physics. In particular, it is possible to get metastable dS minima without adding uplifting terms.