Problem with SP Grid view rendering in custom web part

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SharePoint

application

Hi, All
I am using SPGridView in custom web part, but It is giving error here base.Render(writer)- error is-- (Web Part appears to be causing a problem. Unable to cast object of type 'Microsoft.SharePoint.WebControls.MenuTemplate' to type 'System.Web.UI.WebControls.Table'.)
Even I commented All SPMenuField code but prob. is persist same.

protected override void Render(HtmlTextWriter writer)
        {
            using (SPSite _Site = new SPSite(SPContext.Current.Site.ID))
            {
                using (SPWeb _Web = _Site.OpenWeb())
                {
                    SPSecurity.RunWithElevatedPrivileges(delegate()
                        {
                            if (ChildControlsCreated)
                                spGridView.DataBind();
                            base.Render(writer);
                        });
                }
            }

        }

Below is code example I am using.
spGridView and dataSource are my global object at class label.

protected override void CreateChildControls()
        {

            dataSource = new ObjectDataSource();
            dataSource.ID = "dataSource";
            dataSource.SelectMethod = "GenerateTableTobindGrid";
            dataSource.TypeName = this.GetType().AssemblyQualifiedName;
            dataSource.ObjectCreating += new ObjectDataSourceObjectEventHandler(objectCreating);
            dataSource.Filtering += new ObjectDataSourceFilteringEventHandler(dataSource_Filtering);
            this.Controls.Add(dataSource);

            // SPGridView 
            spGridView = new SPGridView();
            spGridView.ID = "spGridView";
            spGridView.DataSourceID = dataSource.ID;
            spGridView.AutoGenerateColumns = false;
            spGridView.AllowPaging = true;
            spGridView.PageSize = 10;
            spGridView.AllowSorting = true;
            spGridView.EmptyDataText = string.Empty;

           SPMenuField nameCol1 = new SPMenuField();
            nameCol1.HeaderText = "Party";
            nameCol1.TextFields = "Party";
            nameCol1.NavigateUrlFields = "Party";
           nameCol1.SortExpression = "Party";
            nameCol1.MenuTemplateId = "menuTemplate";

           MenuTemplate menuTemplate = new MenuTemplate();
            menuTemplate.ID = "menuTemplate";
            this.Controls.Add(menuTemplate);
            spGridView.Columns.Add(nameCol1);

        MenuItemTemplate mitlUpdPaymt = new MenuItemTemplate("Open WebSite",         "~/_layouts/images/ASP16.GIF");
            //menuItemTemplate1.ClientOnClickNavigateUrl = "javascript:window.open('%KEYWEBSITE%');";
            mitlUpdPaymt.ClientOnClickNavigateUrl = "javascript:OpenPopUp();";
            menuTemplate.Controls.Add(mitlUpdPaymt);

          this.Controls.Add(spGridView);
          this.ChildControlsCreated = true;
       }

If any idea please assist me..
Thanks in Advance.

Arun Kaushik