Web (ASP.NET) ทำไมใส่ปุ่มใน DataList ไม่ได้ อะครับ EnableEventValidation="true" หรือ ต้องทำไงยังใครรู้ช่วยบอกที เถอะ

<%@ Page language="VB" Codebehind="default.aspx.vb" AutoEventWireup="false" Inherits="myWebAppName.Web._default" EnableEventValidation="true"%>

<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" CodeBehind="index.aspx.cs" Inherits="IT_Market.WebForm2"  %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">

 <asp:DataList ID="DataList_pic" runat="server" RepeatColumns="3" 
        RepeatDirection="Horizontal" AllowPaging="True" PageSize="6" 
         CellSpacing="30">
        <ItemTemplate>
            <table style="width:100%; ">
                <tr>
                    <td>
                        <asp:Image ID="Image1" runat="server" 
                            
                            ImageUrl='<%# (Eval("pic") == DBNull.Value)? "images/no_picture.gif" : String.Format("image_show1.aspx?id={0}",Eval("id")) %>' 
                            Width="150px" Height="150px" />
                    </td>
                </tr>
                <tr>
                    <td align="center">
                        ชื่อสินค้า :&nbsp;
                        <asp:Label ID="Label1" runat="server" Text='<%# Eval("name") %>'></asp:Label>
                    </td>
                </tr>
                <tr>
                    <td align="center">
                        ราคา&nbsp;:
                        <asp:Label ID="Label2" runat="server" Text='<%# Eval("price") %>'></asp:Label>
                        &nbsp;บาท</td>
                </tr>
                <tr>
                    <td align="center" >
                        <table style="width:100%;">
                            <tr>
                                <td align="right"><img src="design/btndetail.png" width="70" /></td>
                                <td>&nbsp;<asp:TextBox ID="TextBox1" runat="server" Width="20px" 
                                        ValidationGroup="20"></asp:TextBox>&nbsp;</td>
                                <td align="left">
                                    <asp:ImageButton ID="txtqty" runat="server" ImageUrl="~/design/btnadd.png" 
                                        onclick="txtqty_Click" ValidationGroup="20" Width="80px" 
                                        EnableTheming="True" />
                                </td>
                            </tr>
                        </table>
                    </td>
                </tr>
                <tr>
                    <td align="center">
                        &nbsp;</td>
                </tr>
            </table>
        </ItemTemplate>
        
    </asp:DataList>
</asp:Content>

AutoEventWireup="true" EnableEventValidation="false"