Trailing stoploss

Hi All,

Can someone see whats wrong in my code please? 

            if (TrailingSL)
            {
                if (pos.NetProfit / pos.VolumeInUnits / Symbol.PipSize <= Stoploss)
                {
                    return;
                }
                double newstoploss = pos.TradeType == TradeType.Buy ? Bars.ClosePrices.LastValue - Stoploss * Symbol.PipSize : Bars.ClosePrices.LastValue + Stoploss * Symbol.PipSize;
                newstoploss = Math.Round(newstoploss, Symbol.Digits);

                TradeResult result = ModifyPosition(pos, newstoploss, pos.TakeProfit.Value);

                if (result.IsSuccessful)
                {
                    Print(string.Format("Position {0}: stoploss updated to {1}.", pos.Id, pos.StopLoss.Value));
               

                else
                {
                    Print(string.Format("Position {0}: stoploss could not be updated to {1}.", pos.Id, newstoploss));
                }
            }
        }

It always give a fault in ctrader that the "pos" isn't accepted. 

Thank you,