please look at this carefully
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true">
<table>
<tr>
<td>
<asp:TextBox ID="txt1" runat="server">
</td>
</tr>
//1st grid starts hear
<tr>
<td>
<table>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:GridView ID="grvDemo" runat="server" AllowSorting="true" AutoGenerateColumns="true" EnableSortingAndPagingCallbacks="TRUE">
<Triggers> <asp:AsyncPostBackTrigger ControlID="grvDemo" EventName="grvDemo_Sorting" /> </Triggers>
</ContentTemplate>
</UpdatePanel>
</table>
</td>
</tr>
//1st grid ends &&2nd grid starts hear
<tr>
<td>
<Table>
<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:GridView ID="GridView1" runat="server" AllowSorting="true" AutoGenerateColumns="true" EnableSortingAndPagingCallbacks="TRUE">
<Triggers><asp:AsyncPostBackTrigger ControlID="GridView1" EventName="GridView1_Sorting" /></Triggers>
</ContentTemplate>
</UpdatePanel>
</table>
</td>
</tr>
//2nd grid ends.
</div>
</form>