fileupload control inside Ajax Modal popup extender is not working

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C#

ASP.NET

I have a Datagrid control which displays Id, Image. When I am clicking on edit button a button is there and after click that i want to open a modal popup extender which will be assigned to a panel that contains a fileupload control, ok and cancel button. The problem is when I press the ok button the button_click event I am not able to find the file inside the FileUpload control.

Here is my aspx page code:

<asp:UpdatePanel ID="UpdatePanel1" UpdateMode="Conditional" runat="server">
    <triggers>
        <asp:AsyncPostBackTrigger ControlID="dgnews" />
    </triggers>
    <contenttemplate>
    <asp:DataGrid ID="dgnews" runat="server" AutoGenerateColumns="false" 
                    oncancelcommand="dgnews_cancel" ondeletecommand="dgnews_delete" 
                    oneditcommand="dgnews_edit" onpageindexchanged="dgnews_PageIndexChanged" 
                    onupdatecommand="dgnews_update" Width="715px" AllowPaging="true" 
            AllowSorting="true" DataKeyField="res_id"  PageSize="10" 
            onitemdatabound="dgnews_ItemDataBound" >
                    <pagerstyle horizontalalign="Center" mode="NumericPages">
                         Position="TopAndBottom"/>
                    <columns>
                    <asp:BoundColumn DataField="res_id" Visible="false" HeaderText="">
                            <asp:TemplateColumn HeaderText="Image">
                                <itemtemplate>
                                    <ul style="padding-removed15px;">
                                       <a href="#"><img id="imgSmall" src='<%# DataBinder.Eval(Container, "DataItem.res_image") %>' alt="Gallery Image" width="50" height="50" /></a>
                                    </ul>                                            
                                </itemtemplate>
                                <edititemtemplate>
                                    <asp:Button ID="aaa" Text="Select Images" runat="server"/>
                                        <cc1:ModalPopupExtender BackgroundCssClass="modalBackground"
    CancelControlID="Button2"  runat="server" PopupControlID="picuploader" ID="ModalPopupExtender1"
    TargetControlID="aaa" />
    <asp:Panel ID="picuploader" runat="server" CssClass="modalPopup" DefaultButton="Button1" Style="display:none;">
    <asp:UpdatePanel ID="UpdatePanel2" UpdateMode="Conditional" runat="server">
    <triggers>
    <asp:AsyncPostBackTrigger ControlID="Button1" />
    </triggers>
    <contenttemplate>
            <table>
            <tr>
                <td>
                    <asp:Image Width="50px" Height="50px" ID="Image1" runat="server" /></td>
                <td>
                    <asp:FileUpload ID="FileUpload1" runat="server" /></td>
            </tr>
            <tr>
                <td>
                    <asp:Image Width="50px" Height="50px" ID="Image2" runat="server" /></td>
                <td>
                <asp:FileUpload ID="FileUpload2"   runat="server" /></td>
            </tr>
            <tr>
                <td>
                    <asp:Image ID="Image3" runat="server" Width="50px" Height="50px" /></td>
                <td>
                <asp:FileUpload ID="FileUpload3"   runat="server" /></td>
            </tr>
            <tr>
                <td>
                    <asp:Image ID="Image4" runat="server" Width="50px" Height="50px"/></td>
                <td>
                <asp:FileUpload ID="FileUpload4"  runat="server" /></td>
            </tr>
            <tr>
                <td></td>
                <td><asp:Button ID="Button1" runat="server" Text="ok" OnClick="UploadPic" />
                    <asp:Button ID="Button2" runat="server" Text="cancel" /></td>
            </tr>
            </table>
            </contenttemplate>
</edititemtemplate>         
                <asp:EditCommandColumn CancelText="Cancel" EditText="Edit" HeaderText="Modify" UpdateText="Update"/>
                            <asp:ButtonColumn CommandName="Delete" Text="Delete" HeaderText="Remove"/>                                           
                </columns>
                    
    </pagerstyle></contenttemplate>

and cs is as follows:

ClsCommon cls = new ClsCommon();
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["connectionstring"].ToString());
protected void Page_Load(object sender, EventArgs e)
{
    if (IsPostBack == false)
    {
        BindGrid();
    }
}
protected void BindGrid()
{

}
protected void dgnews_cancel(object source, DataGridCommandEventArgs e)
{
    dgnews.EditItemIndex = -1;
    BindGrid();
}

protected void dgnews_delete(object source, DataGridCommandEventArgs e)
{
    try
    {

    }
    catch (Exception ex)
    {

    }
}

protected void dgnews_edit(object source, DataGridCommandEventArgs e)
{
    dgnews.EditItemIndex = e.Item.ItemIndex;
    BindGrid();
    Session["ID"] = dgnews.DataKeys[e.Item.ItemIndex];
}

protected void dgnews_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
{
    dgnews.CurrentPageIndex = e.NewPageIndex;
    BindGrid();
}

protected void dgnews_update(object source, DataGridCommandEventArgs e)
{

}

protected void UploadPic(object sender, EventArgs e)
{
    if (FileUpload1.PostedFile != null)
    {
        string[] words = FileUpload1.FileName.Split('.');
        string d_name = words[1];
        HttpContext.Current.Session["SessionKey"] = System.Guid.NewGuid().ToString() + "." + d_name;
        cls.UpdateData("_res", new string[] { "res_image" }, new string[] { Session["SessionKey"].ToString() }, "where res_id='" + Session["ID"].ToString() + "'", "Updated Image1", this.Page);
        if (FileUpload1.PostedFile.FileName.Length > 0)
        {
            string imgName = Session["SessionKey"].ToString();
            string imgPath = "../images/Restaurant/" + imgName;
            FileUpload1.SaveAs(Server.MapPath(imgPath));
        }
    }
    if (FileUpload2.PostedFile != null)
    {
        string[] words = FileUpload2.FileName.Split('.');
        string d_name = words[1];
        HttpContext.Current.Session["SessionKey"] = System.Guid.NewGuid().ToString() + "." + d_name;
        cls.UpdateData("_res", new string[] { "res_image2" }, new string[] { Session["SessionKey"].ToString() }, "where res_id='" + Session["ID"].ToString() + "'", "Updated Image2", this.Page);
        if (FileUpload2.PostedFile.FileName.Length > 0)
        {
            string imgName = "2" + Session["SessionKey"].ToString();
            string imgPath = "../images/Restaurant/" + imgName;
            FileUpload2.SaveAs(Server.MapPath(imgPath));
        }
    }
    if (FileUpload3.PostedFile != null)
    {
        string[] words = FileUpload3.FileName.Split('.');
        string d_name = words[1];
        HttpContext.Current.Session["SessionKey"] = System.Guid.NewGuid().ToString() + "." + d_name;
        cls.UpdateData("_res", new string[] { "res_image3" }, new string[] { Session["SessionKey"].ToString() }, "where res_id='" + Session["ID"].ToString() + "'", "Updated Image3", this.Page);
        if (FileUpload3.PostedFile.FileName.Length > 0)
        {
            string imgName = "3" + Session["SessionKey"].ToString();
            string imgPath = "../images/Restaurant/" + imgName;
            FileUpload3.SaveAs(Server.MapPath(imgPath));
        }
    }
    if (FileUpload4.PostedFile != null)
    {
        string[] words = FileUpload4.FileName.Split('.');
        string d_name = words[1];
        HttpContext.Current.Session["SessionKey"] = System.Guid.NewGuid().ToString() + "." + d_name;
        cls.UpdateData("_res", new string[] { "res_image4" }, new string[] { Session["SessionKey"].ToString() }, "where res_id='" + Session["ID"].ToString() + "'", "Updated Image4", this.Page);
        if (FileUpload4.PostedFile.FileName.Length > 0)
        {
            string imgName = "4" + Session["SessionKey"].ToString();
            string imgPath = "../images/Restaurant/" + imgName;
            FileUpload4.SaveAs(Server.MapPath(imgPath));
        }
    }
}

protected void dgnews_ItemDataBound(object sender, DataGridItemEventArgs e)
{
    ListItemType listItemType = e.Item.ItemType;
    if ((listItemType == ListItemType.EditItem) || (listItemType == ListItemType.Item))
    {
        Button imageButton = (Button)e.Item.FindControl("aaa");
        if (imageButton != null)
        {
            UpdatePanel upanel = (UpdatePanel)e.Item.FindControl("UpdatePanel2");
            upanel.Update();
            Image1.ImageUrl = cls.FetchSinglevalue("select res_image from _res where res_id='" + Session["ID"].ToString() + "'");
            Image2.ImageUrl = cls.FetchSinglevalue("select res_image2 from _res where res_id='" + Session["ID"].ToString() + "'");
            Image3.ImageUrl = cls.FetchSinglevalue("select res_image3 from _res where res_id='" + Session["ID"].ToString() + "'");
            Image4.ImageUrl = cls.FetchSinglevalue("select res_image4 from _res where res_id='" + Session["ID"].ToString() + "'");
        }
    }
}