public Form1()
        {
            InitializeComponent();
            Label lbl = new Label();
            lbl.Text = "123";
            lbl.Name = "abc";
            this.Controls.Add(lbl);
            lbl.ContextMenuStrip = this.contextMenuStrip1;
            lbl.MouseDown += new MouseEventHandler(p_MouseDown);
        }
        private void p_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                this.contextMenuStrip1.Items.Clear();
                this.contextMenuStrip1.Items.Add(Control.MousePosition.ToString());
            }
        }
        private void contextMenuStrip1_Opening(object sender, CancelEventArgs e)
        {
            MessageBox.Show((sender as ContextMenuStrip).SourceControl.Name);
        }

------解决方案--------------------
你右击的contextMenuStrip1控件有没有和那个控件绑定，控件的属性里面有个ContextMenuStrip，把它和ContextMenuStrip1控件绑定再试试，比如datagridview控件有个ContextMenuStrip属性，把它绑定到你的ContextMenuStrip1控件中