Extension Method behaving Strangely C#

Question

I have and extension method for Forms.DataVisualization.Charting.Chart. In the extension method I'm accessing the chartareas array and manipulating the chartarea object in it. However, every time I run my code I get an EntryPointNotFoundException.

//This file is in another assembly and is being reference.
namespace Hetco.Forms
{
    public static class ChartingExtensions
    {
        public static void DoSomething( this Chart chart )
    {
            var c = chart.ChartAreas[0];
            c.Position.X = 0;   // Here I get EntryPointNotFoundException here.
            c.AxisY.ScrollBar.ButtonColor = Color.FromArgb(105, 96, 81);
    }
    }
}

//In another module
private System.Windows.Forms.DataVisualization.Charting.Chart c = new System.Windows.Forms.DataVisualization.Charting.Chart();
c.ChartAreas.Add(somechart);
c.DoSomething();

However, If I added the following code

//In another module
private System.Windows.Forms.DataVisualization.Charting.Chart c = new System.Windows.Forms.DataVisualization.Charting.Chart();
c.ChartAreas.Add(somechart);
var a = c.ChartAreas[0];
a.Position.X = 0;
c.DoSomething();

I don't get the EntryPointNotFoundException but I get a NullReferenceException at

    `c.AxisY.ScrollBar.ButtonColor = Color.FromArgb(105, 96, 81); //in the extension` method.

I can avoid that exception by calling that code before c.DoSomething() but I want to be able to use the extension method. I'm using c# 4.0. I probably forgot to do something but I just don't know what.