<form id="frmMaster" method="post" runat="server" enctype="multipart/form-data">
    <asp:ToolkitScriptManager ID="tsManager" AsyncPostBackTimeout="7200" EnableScriptGlobalization="true" EnableScriptLocalization="true" runat="server">
    </asp:ToolkitScriptManager>
<asp:UpdatePanel runat="server" ID="container">
        <ContentTemplate>
<asp:AsyncFileUpload ID="afuAllegato" runat="server" CssClass="testo" 
                                            UploaderStyle="Modern" PersistFile="True" 
                                            onclientuploadcomplete="UploadComplete" onclientuploadstarted="StartUpload" />