Please help with viewgrid onrowupdating problem

<asp:gridview id="GridView1" runat="server" allowpaging="True" 
="" allowsorting="True" autogenerateeditbutton="True" autogeneratedeletebutton="True" alternatingrowstyle-backcolor="#99CCFF" datasourceid="LinqDataSource1" autogeneratecolumns="False" datakeynames="Month_End_Date" onrowdatabound="OnRowDataBound" onrowupdating="OnRowUpdating">
                 <alternatingrowstyle backcolor="#99CCFF">
                 <columns>
                     <asp:boundfield datafield="Month_End_Date" headertext="Month_End_Date" 
="" readonly="True" sortexpression="Month_End_Date">
                     <asp:boundfield datafield="User_Id" headertext="User_Id" readonly="True" 
="" sortexpression="User_Id">
                     <asp:boundfield datafield="Lock_Modified" headertext="Lock_Modified" 
="" readonly="True" sortexpression="Lock_Modified">
                     <asp:boundfield datafield="Lock" headertext="Lock" readonly="True" 
="" sortexpression="Lock">
                    <asp:templatefield headertext="LockYes">
                        <itemtemplate>
                            <asp:label id="lblLockYes" runat="server" text="<%# Bind("Lock") %>">
                        
                        <edititemtemplate>
                            <asp:label id="lblLockYes" runat="server" text="<%# Bind("Lock")%>" visible="true">
                            <asp:dropdownlist 
="" id="ddlLockYes" runat="server" appenddatabounditems="true" datatextfield="Lock" datavaluefield="Lock">

Unable to cast object of type 'System.Web.UI.WebControls.DataControlLinkButton' to type 'System.Web.UI.WebControls.TextBox'.

protected void OnRowUpdating(object sender, GridViewUpdateEventArgs e)
        {

  
            DateTime monthend = DateTime.Parse(((TextBox)GridView1.Rows[e.RowIndex].Cells[0].Controls[0]).Text);
            string drop = dropDownListSelItem;
            //int age = int.Parse(((TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0]).Text);

            //SqlConnection Conn = new SqlConnection(MyGlobals.ConnString);
            //Conn.Open();

            //SqlCommand cmd = new SqlCommand("UPDATE ct_lock SET  lock=@drop where month_end_date=@monthend ", Conn);
            //cmd.Parameters.Add(new SqlParameter("@monthend", monthend));
            //cmd.Parameters.Add(new SqlParameter("@drop", drop));
            //cmd.Parameters.Add(new SqlParameter("@age", age));

            //Conn.Open();
            //cmd.ExecuteNonQuery();
            //Conn.Close();

            //GridView1.EditIndex = -1;
            //fill();





            GridView1.EditIndex = -1;
            GridView1.DataBind();
        }