如何关闭提示窗口

程序运行正常。当提示出现并点击"无效RFID"时，弹出无效RFID消息，我可以再次扫描。但是，如果RFID被接受，我希望提示符自动关闭。在这个程序中，提示符不是自动关闭的。我必须添加什么才能使提示符自动关闭?

private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        string ramses = serialPort1.ReadLine();
        SetRFIDText(ramses);
    }
    private string dotRFID = "";
    private bool shouldClose = false;
    protected void SetRFIDText(string input)
    {
        this.Invoke(new Function(delegate()
        {
            string Hexed = new LasalleRFIDComputerRentals.BLL.DAL.Utils().HexIt(input);
            dotRFID = Hexed.Trim();
            txtRFID.Text = Hexed.Trim();

            if (txtRFID.Text.Trim() == "")
            {
                MessageBox.Show(this, "Please provide the member's RFID.", "Save Member Information", MessageBoxButtons.OK);
                txtRFID.Focus();
                return;
            }
            CustomerInfo customer = new Customer().GetCustomerByRFID(txtRFID.Text);
            if (customer.CustomerID <= 0)
            {
                MessageBox.Show(this, "Incorrect RFID.", "Validation", MessageBoxButtons.OK);
                return;
            }
            else
            {
                txtRFID.Text = "";

                if (_parentForm == "StandBy")
                {
                    Utils.CurrentCustomer.CustomerInfo = customer;
                    frmStandBy form = (frmStandBy)this.Owner;
                    form.xResult = "OK";
                    this.Close();
                }
            }
           }));
    }

我试着在底部(在form.xResult = "OK";下)使用this.Close();，但它最终会挂起。的帮助!