ASP.Net AJAX AsyncFileUpload : Display Success Message using JavaScript alert after File upload

Hi All

i m Uploading File using  Ajax AsyncFileUpload control.. after successfull upload i am trying to dispaly success message through Label and Also through Alert but its not working..below is i used code

 <asp:Panel ID="pnlupload" runat="server" BackColor="LightBlue"
                    CssClass="pnlBackGround" Height="100px" style="display:none" Width="600px">
                       <asp:Label ID="lblmsg" runat="server" Font-Bold="True" Text="" ForeColor="Red"></asp:Label>
                    <table ID="tabid" runat="server" cellpadding="0" cellspacing="0"
                        style="border:Solid 2px #D46900; width:100%; height:100%" width="100%">
                        <tr>
                            <td>
                                <asp:AsyncFileUpload ID="AsyncFileUpload1" runat="server" CompleteBackColor="#66CCFF" OnLoad="AsyncFileUpload1_Load" OnUploadedFileError="AsyncFileUpload1_UploadedFileError" UploadingBackColor="#FFFDF8" Width="80px" onuploadedcomplete="AsyncFileUpload1_UploadedComplete" />
                             <asp:Button ID="update" runat="server" Text="Upload" OnClick="update_click" />
                            </td>
                        </tr>
                        <tr>
                        <td align="center">
                            <asp:Button ID="btnok" runat="server" Text="Close" />
                        </td>
                       
                        </tr>
                    </table>
                </asp:Panel>
                <asp:ModalPopupExtender ID="modalforupload" runat="server"
                     Drag="true" PopupControlID="pnlupload" TargetControlID="btnattach" CancelControlID="btnok" >
                </asp:ModalPopupExtender>

 public void update_click(object sender, EventArgs e)
        {
            if (AsyncFileUpload1.HasFile) // Check the file 
            {

                AsyncFileUpload1.SaveAs(Server.MapPath("~/EmailAttachments/" + AsyncFileUpload1.FileName)); // Save the file 
                lblsub.Text = "<b><blink>" + AsyncFileUpload1.FileName + " " + "Uploaded Successfully" + "</blink><b>";//Not working
               
                ScriptManager.RegisterStartupScript(this, GetType(), "showalert", "alert('"+lblmsg.Text+"');", true); //Not working


            }
        }

how can i dispalay the message and  AsyncFileUpload1

thanks in advance