Percent-change-of-the-charted-symbol-and-the-benchmark-symbols-in-a-new-pane

Hello.
I'm trying to develop code that shows in WL panel the performance of different assets from a specific date.
The code that I used in WL6 so far and that has worked correctly has been:

CODE:
using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using WealthLab;
using WealthLab.Indicators;

namespace WealthLab.Strategies
{
   public class MyStrategy0 : WealthScript
   {
      // Plots the percent change of the charted symbol and the benchmark symbols in a new pane
      public void PlotBenchMarkPct(string[] bmSymbols, Color[] colors, DateTime fromDate)
      {
         int bar = Bars.ConvertDateToBar(fromDate, false);
         //SetBackgroundColor(bar, Color.Black);
         ChartPane cp = CreatePane(1000, false, true);
         DrawLine( cp, bar, 500, bar, -500, Color.Black, WealthLab.LineStyle.Dotted, 1 );
         DrawHorzLine( cp, 0, Color.Black, WealthLab.LineStyle.Dotted, 2 );
         DrawLabel(cp, "Performance from " + fromDate.ToShortDateString(), Color.Navy);
         int c = 0;
         foreach (string sym in bmSymbols)
         {   
            Bars bmBars = GetExternalSymbol(sym, true);            
            double refPrice = bmBars.Close[bar-1];
            DataSeries dsPctChange = 100 * (bmBars.Close/refPrice - 1);
            dsPctChange.Description = sym;
            PlotSeries(cp, dsPctChange, colors[c], WealthLab.LineStyle.Solid, 2);
            c++;
         }
         
      }
      protected override void Execute()
      {
         HideVolume();
         // Show the percent change from a list of symbols from a specified date (1/1/2006)
         string[] benchMarkSymbols = {Bars.Symbol, "^STOXX50E", "EEM"/*, "SDS_D"*/};
         Color[] colors = {Color.Blue, Color.Red, Color.Orange/*, Color.Green*/};
         PlotBenchMarkPct(benchMarkSymbols, colors, new DateTime(2020,03,23));
      }
   }
}

The code that I am trying to get to work on WL7 is as follows:

CODE:
using WealthLab.Backtest;
using System;
using WealthLab.Core;
using WealthLab.Indicators;
using System.Drawing;
using System.Collections.Generic;

namespace WealthScript1 
{
    public class MyStrategy : UserStrategyBase
    {
      // Plots the percent change of the charted symbol and the benchmark symbols in a new pane
      public void PlotBenchMarkPct(string[] bmSymbols, Color[] colors, DateTime fromDate, BarHistory bars)
      {
         int bar = bars.IndexOf(fromDate);
         int c = 0;
         foreach (string sym in bmSymbols)
         {
            BarHistory bmBars = GetHistory (bars, sym);
            double refPrice = bmBars.Close[bar -1];
            TimeSeries dsPctChange = 100 * (bmBars.Close /refPrice - 1);
            dsPctChange.Description = sym;
            PlotTimeSeries(dsPctChange, "% Change", "cp", colors[c], PlotStyles.Line);
            DrawHorzLine(0, Color.Gray, 1, LineStyles.Solid, "cp");
            c++;
         }
         

      }

        public override void Execute(BarHistory bars, int idx)
        {
         // Show the percent change from a list of symbols from a specified date
         string[] benchMarkSymbols = { bars.Symbol, "^GSPC", "EEM"};
         Color[] colors = { Color.Blue, Color.Red, Color.Orange};
         PlotBenchMarkPct(benchMarkSymbols, colors, new DateTime(2020, 03, 23));
      
      }
   }
}

I have two questions:
1.- In line 15, of the WL7 code "bars.IndexOf (fromDate);" it would be the equivalent of "Bars.ConvertDateToBar (fromDate, false);" of WL6?
If not, any suggestions?
2.- What is the reason for the error on line 36? Shouldn't it work the same as the WL6?

Thanks in advance