ajax file upload show error at upload time

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C#

ASP.NET

C#4.0

i am using ajax file upload control ,when i am saving some file in database then no prablem its working fine ,but when i want save some value from dropdown and textbox value at update event then i am getting error,anybody help me ?

my Code is

protected void AjaxFileUpload1_UploadComplete(object sender, AjaxControlToolkit.AjaxFileUploadEventArgs e)
   {
          string filePath = string.Empty;
           filePath = (Server.MapPath("~/Admin/") + Guid.NewGuid() + System.IO.Path.GetFileName(e.FileName));
           AjaxFileUpload1.SaveAs(filePath);
           string strFile = filePath.Substring(filePath.LastIndexOf("\\"));
           string strFileName = strFile.Remove(0, 1);
           string strFilePath = "~/Admin/" + strFileName;
           SqlCommand cmd = new SqlCommand("Insert into tbl_ImageGallery (Image_Name,Imagepath,Category_Id) values (@Image_Name,@Imagepath,@Category_Id)", con);
           cmd.Parameters.AddWithValue("@Image_Name", strFileName);
           cmd.Parameters.AddWithValue("@Imagepath", strFilePath);
           cmd.Parameters.AddWithValue("@Category_Id",dropcategory.SelectedItem.Value);
           con.Open();
           cmd.ExecuteNonQuery();
           con.Close();
           cmd.Dispose();


   }

dropdownlist controls value is not taking .