private void cmdModifyPrivilege_Click(object sender, EventArgs e)
        {
            int     vEnrollNumber;
            int     vEMachineNumber;
            int     vFingerNumber;
            int     vMachinePrivilege;
            Boolean vRet;
            int     vErrorCode = 0;

            lblMessage.Text = "Working...";
            Application.DoEvents();

            vEMachineNumber   = cmbEMachineNumber.SelectedIndex + 1;
            vEnrollNumber     = Convert.ToInt32(txtEnrollNumber.Text);
            vFingerNumber     = Convert.ToInt32(cmbBackupNumber.Text);
            vMachinePrivilege = Convert.ToInt32(cmbPrivilege.Text);

            vRet = bpc.EnableDevice(Program.gMachineNumber, 0); // 0 : false
            if (!vRet)
            {
                lblMessage.Text = util.gstrNoDevice;
                return;
            }

            vRet = bpc.ModifyPrivilege(Program.gMachineNumber, vEnrollNumber, vEMachineNumber, vFingerNumber, vMachinePrivilege);
            if (vRet)
            {
                lblMessage.Text = "Success!";
            }
            else
            {
                bpc.GetLastError(ref vErrorCode);
                lblMessage.Text = util.ErrorPrint(vErrorCode);
            }

            bpc.EnableDevice(Program.gMachineNumber, 1); // 1 : true
        }