It appeares the "MouseEventArg e" is sometimes passed as null to...
Infragistics.Win.UltraWinChart.UltraChart.SendEvents(Primitive p, MouseEventArgs e)
causing the crash (about 1 in 6) on our testing (using middle mouse button)

After I make some source changes in UltraChart.cs, that moves the base.OnMousedown()  to after the Tools.MouseDown, the Mouse arguments are no longer randomly null in SendEvents

Below I have included my chages to UltraChart.cs:OnMOuseDown line 5967

        protected override void OnMouseDown(MouseEventArgs evt)
        {
            this.lastInput.ViewPoint = new Point(evt.X, evt.Y);
            this.lastInput.Buttons = evt.Button;
            this.lastInput.Modifiers = Control.ModifierKeys;
            this.lastInput.MouseEventArgs = evt;

            if (this.AcceptsFocus)
            {
                // RequestFocus();

                //MAC crash in UltraChart.SendEvents originate here
                //System.NullReferenceException: Object reference not set to an instance of an object.
                //at Infragistics.Win.UltraWinChart.UltraChart.SendEvents(Primitive p, MouseEventArgs e)
                //at Infragistics.Win.UltraWinChart.DefaultTool.MouseDown()
                //at Infragistics.Win.UltraWinChart.UltraChart.OnMouseDown(MouseEventArgs evt)
                //at System.Windows.Forms.Control.WmMouseDown(Message& m, MouseButtons button, Int32 clicks)
                //MAC I belive base.OnMouseDown should be after Tool.Mousedown because
                //MAC sometimes evt is null inside SendEvents(p,e) 
                //MAC garbage collection?
                //base.OnMouseDown(evt);
                //MAC

                this.Tool.MouseDown();

                //MAC
                base.OnMouseDown(evt);
                //MAC
             
            }

            this.lastInput.MouseEventArgs = null;
        }