Right Click in TreeView not responding

[bixel]

C# WinForms.. trying to get a contextMenu to show in TreeView when I right click - but nothing is happening

        private void mainView_MouseClick(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                if (mainView.SelectedNode == null)
                {
                    Point ClickPoint = new Point(e.X, e.Y);
                    Point ScreenPoint = mainView.PointToScreen(ClickPoint);
                    Point FormPoint = this.PointToClient(ScreenPoint);
                    cntxtMenuTreeNPCCreate.Show(this, FormPoint);
                }
            }
        }