multiple update panels in one page not working properly

Question

Dear Reader thanks in advance for ur consideration.

 I am using two update panels in single aspx page

like

<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional" >

<ContentTemplate>

<table border="0" cellspacing="0" cellpadding="5">

<tr>

 <td  >

<asp:DropDownList ID="cBoxSiteName" runat="server" AutoPostBack="true"  OnSelectedIndexChanged="cBoxSiteName_SelectedIndexChanged"  >

</asp:DropDownList>

</td>

</tr>

</table>

 </ContentTemplate>

</asp:UpdatePanel>

 

 

<asp:UpdatePanel ID="UpdatePanel2" runat="server" >

<ContentTemplate>

 

<asp:GridView ID="GridView1"  AutoGenerateColumns="False" ShowHeaderWhenEmpty="true"

 AllowPaging="true" AllowSorting="false" ShowFooter="false"

OnPageIndexChanging="GridView1_PageIndexChanging" OnRowDataBound="GridView1_RowDataBound">

 

<asp:Timer ID="ServerTimer" runat="server" Interval="3000" OnTick="ServerTimer_OnTick">

</asp:Timer>

 

</ContentTemplate>

</asp:UpdatePanel>

 -------------------------------------------------------------------------------------------------------------

on timer tick gridview shows nothing but it has data to show . and on changing the drop down value also same problem 

Can any one help ?? your response is highly appreciated. thanx