This package is not maintained and very poorly written. I would suggest either using PyMultinest which calls the Multinest Library or Nestle which is a pure Python implementation
F. FEROZ, M.P. HOBSON, "MULTIMODAL NESTED SAMPLING: AN EFFICIENT AND ROBUST ALTERVATIVE TO MCMC METHODS FOR ASTRONOMICAL DATA ANALYSIS" Mon. Not. Roy. Astron. Soc., 384, 2, 449-463 (2008)
F. FEROZ, M.P. HOBSON, M. BRIDGES, "MULTINEST: AN EFFICIENT AND ROBUST BAYESIAN INFERENCE TOOL FOR COSMOLOGY AND PARTICLE PHYSICS" Mon. Not. Roy. Astron. Soc. 398: 1601-1614 (2009)