I looked at the code for this over and over and it seems like something is missing but I can not see the difference when comparing your example.

m_VerticalAxisCursor = new NAxisCursor();
m_VerticalAxisCursor.BeginEndAxis = (int)StandardAxis.PrimaryX;
m_VerticalAxisCursor.ValueChanged += new EventHandler(OnValueChanged);
m_VerticalAxisCursor.ValueSnapper = new NAxisRulerClampSnapper();
m_VerticalAxisCursor.SynchronizeOnMouseAction |= MouseAction.Move;

for (int i = 0; i < MainList.Count(); i++)
{
NAxis primaryXAxis = MainList[i].Item1.Axis(StandardAxis.PrimaryX);
primaryXAxis.Cursors.Clear();
primaryXAxis.Cursors.Add(m_VerticalAxisCursor);
}

nChartControl1.Controller.Tools.Clear();
nChartControl1.Controller.Tools.Add(m_DataCursorTool);


The event for the value changed never gets hit. Also when I click the chart plot area it shows a vertical line where I clicked, I don't see where that's coming from.