Mine

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!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>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server" >
    <asp:ScriptManager runat="server"  ID="sm1" />
    <asp:UpdatePanel ID="Updatepanel1"  runat="server" UpdateMode="Conditional">
    
    <ContentTemplate>
    <div>
    <asp:DropDownList ID="ddl1" runat="server" AutoPostBack="true" onSelectedIndexChanged="ddl1_Click">
    </asp:DropDownList>
    <asp:PlaceHolder runat="server" ID="Placeholder1" >
    </asp:PlaceHolder>
    <asp:PlaceHolder ID="Placeholder2" runat="server">
    </asp:PlaceHolder>
    </div>
    </ContentTemplate>
    <Triggers>
    <asp:AsyncPostBackTrigger ControlID="ddl1" EventName="SelectedIndexChanged" />
    </Triggers>
    </asp:UpdatePanel>
    
    </form>
</body>
</html>



using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{
    public int nrOfControls
    {
        get
        {
            if (Session["nrControls"] == null)
                Session["nrControls"] = 0;

            return (int)Session["nrControls"];
        }
        set { Session["nrControls"] = value; }
    }

    protected void Page_Init(object sender, EventArgs ea)
    {
        ListItem li; 
        if (!IsPostBack)
        {
            nrOfControls = 0;
        }
        for (int i = 0; i <= 5; i++)
        {
            li = new ListItem(i.ToString());
            ddl1.Items.Add(li);
        }
        LoadControls();
    }

    protected void ddl1_Click(object sender, EventArgs ea)
    {
        nrOfControls = int.Parse(ddl1.SelectedValue);

        //Remove previously created fileupload controls
        for (int i = 0; i < Placeholder1.Controls.Count; i++)
        {
            if (Placeholder1.Controls[i] is FileUpload)
                Placeholder1.Controls.RemoveAt(i--);
        }

        LoadControls();
    }

    private void LoadControls()
    {
        FileUpload fu;
        for (int i = 0; i < nrOfControls; i++)
        {
            fu = new FileUpload();
            fu.Style.Add("display", "block");
            fu.ID = "fu" + i;
            Placeholder1.Controls.Add(fu);
        }
    }

    void b_Click(object sender, EventArgs e)
    {
        Label lbl = new Label();
        lbl.ID = "lbl1";

        lbl.Text = "lbl ";
        
        foreach (Control c in Placeholder1.Controls)
        {
            if (c is FileUpload)
            {
                //Response.Write(((FileUpload)c).FileName + "<br/>");
                lbl.Text += ((FileUpload)c).FileName;
            }
        }

        Placeholder2.Controls.Add(lbl);
    }

    protected void Page_Load(object sender, EventArgs e)
    {
        if (int.Parse(ddl1.SelectedValue) > 0)
        {
            Button b;

            b = new Button();
            b.ID = "b1";
            b.Text = "Submit";
            b.Click += new EventHandler(b_Click);
            Placeholder2.Controls.Add(b);
            Updatepanel1.Triggers.Add(Upsite.CodeBlocks.getTrigger(b,"Click"));
            
        }
    }
}