ASP.Net FileUpload control does not work when placed inside UpdatePanel

Hi sir,

Following is my html design

<asp:UpdatePanel ID="up1" runat="server"> <ContentTemplate>     <asp:FileUpload ID="FileUpload1" runat="server" /> <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="upload" /> <asp:Label ID="Label1" runat="server" Text=""></asp:Label>    </ContentTemplate> </asp:UpdatePanel>

and

if (FileUpload1.PostedFile !=null)         {

//my upload code here....

}

without update panel it works fine

after place all control inside update its not working. How to fix this...