首先，感谢那些提供反馈的人。
经过多次尝试，例如。创建并在任务中显示用户提示窗口，我发现使其工作的方法是在应用程序调度器上下文中运行代码。同样，使用线程的整个解决方案是过时的，将来某个时候将更新为使用Tasks，但目前有效的解决方案使用 Application.Current.Dispatcher. Dispatcher（） 和 System.Windows.Application.Current. Dispatcher. Dispatcher（DispatcherPriority.Background，new Action（delegate { }））的组合来确保窗口在UI线程中创建和显示; 允许窗口的UI在等待用户关闭窗口时运行，或者确定用户已经取消（停止）当前正在执行的操作序列。
下面是生成的代码：

/// <summary>
    /// Executes the sequence.  Shows the given string in to the user.
    /// </summary>
    /// <returns></returns>
    public override bool Execute()
    {
        bool bActionResult = true;

        string sMessageString;
        if (!GetStringFromParm("CmiActionMessageBox", m_StringToShow, out sMessageString))
        {
            return false;
        }

        if (this.ConvertEscapeSequences)
        {
            sMessageString = this.GetStringConvertEscapeSequences(sMessageString);
        }

        bool? dr = ShowMessageBox(sMessageString);

        if (m_bDialogSavesResult)
        {
            if (dr == true)
            {
                SequenceMgr.Mgr.SetVariableValue(m_sDialogResultVar, "True");
            }
            else
            {
                SequenceMgr.Mgr.SetVariableValue(m_sDialogResultVar, "False");
            }
        }

        if (m_bDialogCanStopSequence)
        {
            if (dr == false)
            {
                bActionResult = false;
            }
        }

        return bActionResult;
    }

    /// <summary>
    /// Shows the message box
    /// </summary>
    /// <param name="sMessageString"></param>
    /// <returns></returns>
    private bool? ShowMessageBox(string sMessageString)
    {
        bool? dr = null;

        System.Windows.Application.Current.Dispatcher.Invoke(new Action(() =>
        {
            UserPromptWindow userPromptWindow = new UserPromptWindow(sMessageString);
            userPromptWindow.SetOKButtonText(m_sOkButtonName);
            userPromptWindow.SetCancelButtonText(m_sCancelButtonName);
            userPromptWindow.WindowStartupLocation = WindowStartupLocation.CenterOwner;

            if (m_bDialogIsModal)
            {
                dr = userPromptWindow.ShowDialog();
            }
            else
            {
                try
                {
                    userPromptWindow.Show();

                    // Wait until it goes away
                    while (userPromptWindow.ModelessResult == null)
                    {
                        // Let the UI events run
                        GlobalMethods.WpfApplicationsDoEvents();

                        // Did the user press the stop button?
                        if (SequenceMgr.Mgr.BgSequenceDone)
                        {
                            userPromptWindow.ModelessResult = false;

                            // Close the window, if it is still open
                            if (userPromptWindow.IsLoaded)
                            {
                                userPromptWindow.Close();
                            }

                            break;
                        }
                    }
                }
                catch (Exception e)
                {
                    SystemEventsMgr.AddException("Exception in MessageBox sequence action", e);
                    userPromptWindow.ModelessResult = false;
                }

                dr = userPromptWindow.ModelessResult;
            }
        }));

        return dr;
    }