The file is attached is invalid

See more:

C#

ASP.NET

Ajax

Here I use ajax fileupload.when select the file the error is occured like "unhandled exception.The file attached is invalid".

<asp:DataList ID="DataList1" runat="server" RepeatDirection="Horizontal"         RepeatColumns="4" width="100%"  >
  <ItemTemplate>	
  <table width="98%" border="0" cellspacing="0" cellpadding="0" align="center">
  <tr>
  <td align="center">
  <asp:ImageButton ID="gallery" runat="server"  ImageUrl='<%# Eval("photo") %>'    width="180" height="200" CssClass="img-responsive img-thumbnail" />
 <asp:AsyncFileUpload ID="AsyncFileUpload1" runat="server" Width="180" CompleteBackColor="White"  ThrobberID="imgLoad" OnUploadedComplete="doUpload"  />
  <asp:Image ID="imgLoad" runat="server" imgurl="loading.jif"  Visible="false"/>
  
  <asp:Label ID="imageid" runat="server" Text='<%#Eval("proimg_id") %>'                         Visible="false" ></asp:Label>
  
  </td>
  </tr>
  <tr>
    <td align="center"> </td>
    
  </tr>
  <tr>
     <td align="center"> </td>
   </tr>
          </table>
		 
</ItemTemplate>
 </asp:DataList>

public void gallery()
  {
      try
      {
          DataSet ds = new DataSet();
          obj.type = 4;
         //select photo,proimg_id from tbl_photos
          ds = obj.bind();
          DataList1.DataSource = ds;
          DataList1.DataBind();
      }
      catch(Exception ex)
      {
          Response.Write (ex.ToString());
      }
    }

 protected void doUpload(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e)
 {
   AjaxControlToolkit.AsyncFileUpload lbl =(AjaxControlToolkit.AsyncFileUpload)sender;
   DataListItem container = (DataListItem)lbl.NamingContainer;
   Label imageid1 = (Label)container.FindControl("imageid");
   obj.proimgid = int.Parse(imageid1.Text);
   AsyncFileUpload file1 = (AsyncFileUpload)container.FindControl("AsyncFileUpload1");
   b = file1;
   filename1 = b.PostedFile.FileName;
   b.SaveAs(Server.MapPath("../Upload/" + filename1));
   obj.photoname = "../Upload/" + filename1.ToString();
   obj.type = 5;
   result=obj.Execute();
   //update query 
   //update tbl_photos set photo=@photoname where proimg_id=@proimgid 
   if (result > 0)
      {
          gallery();  
      }
 }

i add clientidmode="autoid". but it does not work properly.how to solve this?
then i use .net 3.5 version