Mass balance error

I have set a reservoir model with w2 ver 3.71. I have activated six water quality paprameters including PO4, NH4, NO3, CBOD, Algae and DO. But three parameters PO4, NH4 and DO are calculated zero from the first day of simulation. Snp file shows error in mass balance calculation for these constituents (CMBRS is NaN). I also checked with ver3.6 and no difference in results was seen. I appreciate anyone could solve this problem for me.