Losing the dynamically created uploadfile on postback ?

hi anyhelp i lose my dynamically created uploadfile when it postback. how can i fix this error heres my code

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ofw_regs.aspx.cs" Inherits="ofw_regs" EnableViewState="true" EnableEventValidation="true" %>
<%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="asp" %>
<%@ Register TagPrefix="MyControls" Namespace="MyControls" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>OFW SUMMIT 2012</title>
<link href="css/index.css" rel="stylesheet" type="text/css" /> ...