File upload, Page refresh

In the application, I have a web page in which I have a combo box, On selection of the data different pages loaded in the iFrame. In the parent page I have a LinkButton, on click of Button the upload page is called. On click of Attached the attached files should be shown in the grid. This casses the page postback and the data on the page is lost. Kindly suggest the workaround.

<div>
   <table>
      <tr>
         <td>
           <asp:UpdatePanel ID="UpdatePanel1" runat="server">
           <ContentTemplate>
           <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_Se ...