DataGrid分页问题，无法显示第二页数据

大家好，我程序中的DataGrid分页无法显示第二页数据。具体症状可以见如下链接地址：

http://www.infozobo.com/persons/1/2.html

代码如下：
.aspx文件
<atlas:UpdatePanel ID="upPostBack" runat="server"><Triggers><atlas:ControlEventTrigger ControlID="btnSend" EventName="Click"/></Triggers>
<ContentTemplate>
<table border="0" cellpadding="0" cellspacing="0" style="width: 920px;margin:auto" >
<tr><td>

<asp:DataGrid ID="dgPersonBack" runat="server" AllowPaging="True" AutoGenerateColumns="False" ShowHeader="False" Width="920px" OnItemDataBound="dgPersonBack_ItemDataBound" OnPageIndexChanged="dgPersonBack_PageIndexChanged" BorderColor="Silver" BorderStyle="Solid" BorderWidth="1" GridLines="None" >

<PagerStyle Font-Bold="False" Font-Italic="False" Font-Overline="False" Font-Strikeout="False"
Font-Underline="False" HorizontalAlign="Right" Mode="NumericPages" Position="TopAndBottom" />
<Columns>
<asp:BoundColumn DataField="id" ReadOnly="True" Visible="False"></asp:BoundColumn>

<asp:TemplateColumn>
<ItemTemplate>
<table border="0" cellpadding="0" cellspacing="0" class="bordercolor" style="width: 920px">
<tr style="background-color:darkgray;height:20px;color:darkblue">
<td style="width:10%"><asp:Label ID="lblLou" runat="server"></asp:Label>
</td><td style="width:30%">作者：<%#Eval("sender") %></td><td style="width:30%">时间：<%#Eval("sendtime") %></td>
<td align="right">
<a href="delete-<%#Eval("id")%>.html">删除</a></td>
</tr>
</table>
<table border="0" cellpadding="0" cellspacing="0" class="bordercolor" style="width: 920px">
<tr><td colspan="2" style="width: 100%; height: 30px;font-size:small" valign="middle">
<%#Eval("info") %>
</td>
</tr>

</table>
</ItemTemplate>
</asp:TemplateColumn>

</Columns>
</asp:DataGrid>
</td></tr>
</table>
</ContentTemplate>
</atlas:UpdatePanel>


.cs文件代码：
protected void BindGrid()
{
string sqlSelect = "select * from personback where personid='" + Request.QueryString["personid"] + "'";
DataSet ds = db.GetDs(sqlSelect);
dgPersonBack.DataSource = ds;
dgPersonBack.DataBind();
}
protected void dgPersonBack_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
{
dgPersonBack.CurrentPageIndex = e.NewPageIndex;
BindGrid();
}