Problem in event within a combo added to adxOlExplorerCommandBar1

   public class AddinModule : AddinExpress.MSO.ADXAddinModule
    {
        public AddinModule()
        {
            InitializeComponent();
        }

        private AddinExpress.MSO.ADXOlExplorerCommandBar adxOlExplorerCommandBar1;
        private AddinExpress.MSO.ADXCommandBarPopup mnu_File;
        private AddinExpress.MSO.ADXCommandBarButton file_Btn;
        private AddinExpress.MSO.ADXCommandBarComboBox file_combo;
 
        #region Component Designer generated code
        /// <summary>
        /// Required by designer
        /// </summary>
        private System.ComponentModel.IContainer components;
 
        /// <summary>
        /// Required by designer support - do not modify
        /// the following method
        /// </summary>
        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.adxOlExplorerCommandBar1 = new AddinExpress.MSO.ADXOlExplorerCommandBar(this.components);
            this.mnu_File = new AddinExpress.MSO.ADXCommandBarPopup(this.components);
            this.file_Btn = new AddinExpress.MSO.ADXCommandBarButton(this.components);
            this.file_combo = new AddinExpress.MSO.ADXCommandBarComboBox(this.components);
            // 
            // adxOlExplorerCommandBar1
            // 
            this.adxOlExplorerCommandBar1.CommandBarName = "adxOlExplorerCommandBar1";
            this.adxOlExplorerCommandBar1.CommandBarTag = "70e3d7e6-886c-4b8b-8502-2795443edb11";
            this.adxOlExplorerCommandBar1.Controls.Add(this.mnu_File);
            this.adxOlExplorerCommandBar1.Temporary = true;
            this.adxOlExplorerCommandBar1.UpdateCounter = 3;
            // 
            // mnu_File
            // 
            this.mnu_File.Caption = "File";
            this.mnu_File.Controls.Add(this.file_Btn);
            this.mnu_File.Controls.Add(this.file_combo);
            this.mnu_File.ControlTag = "713c7999-9bb4-4071-ab82-808310c37755";
            this.mnu_File.Temporary = true;
            this.mnu_File.UpdateCounter = 2;
            // 
            // file_Btn
            // 
            this.file_Btn.Caption = "btn1";
            this.file_Btn.ControlTag = "3c6db618-decb-4372-bb13-ca5d34ebc71c";
            this.file_Btn.ImageTransparentColor = System.Drawing.Color.Transparent;
            this.file_Btn.Temporary = true;
            this.file_Btn.UpdateCounter = 2;
            this.file_Btn.Click += new AddinExpress.MSO.ADXClick_EventHandler(file_Btn_Click);
            // 
            // file_combo
            // 
            this.file_combo.Caption = "combo";
            this.file_combo.ControlTag = "3ba94cb3-4bf6-400c-b07e-461c16649d0e";
            this.file_combo.Items.AddRange(new string[] {
            "one",
            "two",
            "three",
            "four"});
            this.file_combo.Temporary = true;
            this.file_combo.UpdateCounter = 4;
            this.file_combo.Change += new AddinExpress.MSO.ADXChange_EventHandler(file_combo_Change);
            // 
            // AddinModule
            // 
            this.AddinName = "MyAddin1";
            this.SupportedApps = AddinExpress.MSO.ADXOfficeHostApp.ohaOutlook;

        }


        #endregion
 
        #region Add-in Express automatic code
 
        // Required by Add-in Express - do not modify
        // the methods within this region
 
        public override System.ComponentModel.IContainer GetContainer()
        {
            if (components == null)
                components = new System.ComponentModel.Container();
            return components;
        }
 
        [ComRegisterFunctionAttribute]
        public static void AddinRegister(Type t)
        {
            AddinExpress.MSO.ADXAddinModule.ADXRegister(t);
        }
 
        [ComUnregisterFunctionAttribute]
        public static void AddinUnregister(Type t)
        {
            AddinExpress.MSO.ADXAddinModule.ADXUnregister(t);
        }
 
        public override void UninstallControls()
        {
            base.UninstallControls();
        }

        #endregion

        public Outlook._Application OutlookApp
        {
            get
            {
                return (HostApplication as Outlook._Application);
            }
        }

        private void file_Btn_Click(object sender)
        {
            System.Windows.Forms.MessageBox.Show("btn click");
        }

        void file_combo_Change(object sender)
        {
            System.Windows.Forms.MessageBox.Show(file_combo.Text);

        }

    }