<asp:ScriptManager ID="aa" runat="server"/>
     <asp:UpdatePanel ID="UpdatePanel1" runat="server">
         <ContentTemplate>
             <asp:GridView ID="GridView1" runat="server">
             </asp:GridView>
         </ContentTemplate>
        
              </asp:UpdatePanel>

------解决方案--------------------
HTML code

 <asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
              <%-- <asp:Panel ID="Panel1" runat="server">--%>
                    <asp:GridView ID="GridView1" runat="server"  GridLines="None" Width="81%" 
                        AutoGenerateColumns="False">
                        <Columns>
                            <asp:TemplateField HeaderText="Payment Phase">
                                <ItemTemplate>
                                    <asp:Label ID="Label1" Text='<%#Eval("pp") %>' runat="server"></asp:Label>
                                </ItemTemplate>
                                <HeaderStyle HorizontalAlign="left"  Width="8%" />
                            </asp:TemplateField> 
                            <asp:TemplateField HeaderText="Payment Date">
                      <ItemTemplate>
                    <asp:TextBox ID="yyyy" MaxLength="4" Width="85px" runat="server" Text='<%# Eval("yyyy") %>'></asp:TextBox>-
                        <%--  <asp:T