Asynchronous fileUpLoad control error in ajax tool kit control

Question

i am using the ajax tool kit asynchronous file upload control  i drag and drop from the tool bar then run the page with out writing single line of code it display error when i am browse my file the error is

Message from webpage

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Unhandled Exception: The file attached is invalid.

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OK  

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i using the following code : of course i not write even single line of code 

 <asp:UpdatePanel ID="UpdatePanel1" runat="server">
           <ContentTemplate>      
                   <asp:AsyncFileUpload runat="server" ID="AsyncFileUpload1">
               </asp:AsyncFileUpload>
           </ContentTemplate>

           </asp:UpdatePanel>

What is the solution for this