simulation question

Dear users, I am trying to compare several specific PK/PD study designs by: -- run 200 simulations with the final model (develope from original dataset) -- fit the final model to the 200 simulated dataset To achieve above, I used $SIM SUBPROB=200 option however, nonmem would completely stop after running into estimation problem at one specific simulation/estimation cycles, for some designs it stop even before 10th iterations. Is there anyway nonmem could continue go on? Or, does someone know alternative way to achieve the goal? thanks