bool isSelectMode = false;

        private void listView1_ItemCheck(object sender, ItemCheckEventArgs e)
        {
            if (listView1.SelectedItems.Count>1 && isSelectMode)
            {
                e.NewValue = e.CurrentValue;
                isSelectMode = false;
            }
        }

        private void listView1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.Control || e.Shift)
                isSelectMode = true;
        }

        private void listView1_KeyUp(object sender, KeyEventArgs e)
        {
            isSelectMode = false;
        }