Technical Error

I have a strange issue.  While Backtesting using FxPro on 12/10/2018, it is returning a Technical Error when I modify the positions. When the BOt opens a second buy or sell position the OnOpen event modifies the TP of all buy or sell position. If i use the ModifyPosition method directly, it gives me a technical error.  If i use my modified Modify trade procedure it does not. But I don't understand what is causeing the technical error or why their would be a difference.

OnOpen code:

            if (opened.Position.TradeType == TradeType.Buy && BuyCount > 1)
            {    
                 foreach (var position in Positions)
                 {   
                    if (position.TradeType == TradeType.Buy) 
                    ModifyPosition(position, null, RelPrice(10, opened.Position.TradeType));
                    //ModifyTrade("Martingale Buy TP Set: "+position.Label, position, null, RelPrice(10, opened.Position.TradeType));
                 }   
            }
            
            if (opened.Position.TradeType == TradeType.Sell && SellCount > 1)
            {
                foreach (var position in Positions)
                {
                    if (position.TradeType == TradeType.Sell) ModifyTrade("Martingale Sell TP Set: "+position.Label, position, null, RelPrice(9.5, opened.Position.TradeType));
                }
            }

        double RelPrice(double _takeprofitpips, TradeType _tradetype)
        {
            return Math.Round(_tradetype == TradeType.Buy ? AvgPrice(TradeType.Buy) + _takeprofitpips * Symbol.PipSize : AvgPrice(TradeType.Sell) - _takeprofitpips * Symbol.PipSize, 5);
        }

protected override void OnError(Error error)
        {
            switch (error.Code)  
            {
                case ErrorCode.BadVolume:                   
                    _thread = new Thread(() => {MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop);});
                    _thread.SetApartmentState(ApartmentState.STA);
                    _thread.Start();
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: Bad volume for order open, robot is stopped.");
                    RobotStopped = true;
                    break;
                case ErrorCode.EntityNotFound:
                    //_thread = new Thread(() => {MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop );});
                    //_thread.SetApartmentState(ApartmentState.STA);
                    //_thread.Start();
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: Entity Not Found.");
                    //RobotStopped = true;
                    break;
                case ErrorCode.TechnicalError:
                    _thread = new Thread(() => {MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop );});
                    _thread.SetApartmentState(ApartmentState.STA);
                    _thread.Start();
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: Technical Error.");
                    //RobotStopped = true;
                    break;
                case ErrorCode.NoMoney:
                    MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop );
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: No money for order open, robot is stopped.");
                    RobotStopped = true;
                    break;
                case ErrorCode.Disconnected:
                    MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop );
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: Disconnected.");
                    break;
                case ErrorCode.MarketClosed:
                    MessageBox.Show("ErrorCode: " +error.Code.ToString(), Account.BrokerName+" - "+this.ToString(), MessageBoxButtons.OK, MessageBoxIcon.Stop );
                    Log(paramIntLogEnable, paramExtLogEnable,"ErrorCode: The market is closed.");
                    break;
            }
        }

Is there anyway to get more error information to understand what is causing the technical error??