  Charm particle production in nucleus-nucleus collisions at the CERN SPS
energies is considered within a statistical approach. Namely, the Statistical
Model of the Early Stage is used to calculate mean multiplicity of charm
particles in central Pb+Pb collisions. A small number of produced charm
particles necessitates the use of the exact charm conservation law. The model
predicts a rapid increase of mean charm multiplicity as a function of collision
energy. The mean multiplicity calculated for central Pb+Pb collisions at the
center of mass energy per nucleon pair $\sqrt{s_{NN}}=17.3$ GeV exceeds
significantly the experimental upper limit. Thus, in order to describe open
charm production model parameters and/or assumptions should be revised.
