yes thanks, I should learn to do my research first before impulsively posting

it seems that the error is caused by the fact that one parameter is set at -1 in the par file. therefore I get the error every time I test the par files are read (like test or retraining)

this occurs when a ratio like PF is optimized and there are no losing trades in the best parameter of the training set, which can happen for short train cycles

here is my solution for the objective function, in case anyone might stumble upon the same problem:
if(!NumLossTotal)
{
if(NumWinTotal) return NumWinTotal;
return 0;
}
else
return ThisPerformance.vWin/abs(ThisPerformance.vLoss);