Menu item added to Excel cannot be called twice

I'm using Visual Studio for office to create an Excel Addin.  I've created a sample menu, with 2 methods.  If I select a menu item, it displays my dialog box.  After I close it my menu will not display again.  It won't drop down when clicked on.  Do you know why?

If you click choice1 or choice2, then you are done, can't do it twice.  Code below:
        private void ThisAddIn_Startup(object sender, System.EventArgs e)
        {
            #region VSTO generated code
            this.Application = (Excel.Application)Microsoft.Office.Tools.Excel.ExcelLocale1033Proxy.Wrap(typeof(Excel.Application), this.Application);
            #endregion

            CheckIfMenuBarExists();
            AddMenuBar();
        }

        // Create the menu, if it does not exist.
        private void AddMenuBar()
        {
            try
            {
                Office.CommandBarButton menuCommand;

                Office.CommandBarPopup cmdBarControl = null;
                Office.CommandBar menubar = (Office.CommandBar)Application.CommandBars.ActiveMenuBar;
                int controlCount = menubar.Controls.Count;
                string menuCaption = "&Stockwatch Quotes";

                // Add the menu.
                cmdBarControl = (Office.CommandBarPopup)menubar.Controls.Add(
                    Office.MsoControlType.msoControlPopup, missing, missing, controlCount, true);

                if (cmdBarControl != null)
                {
                    cmdBarControl.Caption = menuCaption;
                    Office.CommandBarButton m1, m2;

                    // Add the menu command.
                    m1 = (Office.CommandBarButton)cmdBarControl.Controls.Add(
                        Office.MsoControlType.msoControlButton, missing, missing, missing, true);
                    m1.Caption = "&Choice 1...";
                    m1.Tag = "choice1";
                    m1.FaceId = 65;
                    m1.Click += new Microsoft.Office.Core._CommandBarButtonEvents_ClickEventHandler(
                        choice1_Click);
                    m2 = (Office.CommandBarButton)cmdBarControl.Controls.Add(
                        Office.MsoControlType.msoControlButton, missing, missing, missing, true);
                    m2.Caption = "&Choice 2...";
                    m2.Tag = "choice2";
                    m2.FaceId = 65;
                    m2.Click += new Microsoft.Office.Core._CommandBarButtonEvents_ClickEventHandler(
                        choice2_Click);
                }
            }
            catch (Exception e)
            {
                MessageBox.Show(e.Message);
            }
        }

        private void choice1_Click(Microsoft.Office.Core.CommandBarButton Ctrl, ref bool CancelDefault)
        {
            MessageBox.Show("Choice 1");
            CancelDefault = false;
        }
        private void choice2_Click(Microsoft.Office.Core.CommandBarButton Ctrl, ref bool CancelDefault)
        {
            MessageBox.Show("Choice 2");
            CancelDefault = false;
        }
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