protected void btnElencoIscritti_Click(object sender, System.EventArgs e)
    {
        Button btnElencoIscritti = (Button)sender;
        string id = btnElencoIscritti.CommandArgument.ToString();

        Corso corso = new Corso(id);
        Corso.esportaIscritti(id); //Qui mi creo il file xls

        // The file path to download.
        string filepath = Utility.PERCORSO_FISICO("/" + Costanti.PERCORSO_TEMP + Utility.RewritelUrl(corso.Titolo, "-") + ".xls");

        // The file name used to save the file to the client's system..
        string filename = Path.GetFileName(filepath);
        System.IO.Stream stream = null;
        try
        {
            // Open the file into a stream.
            stream = new FileStream( filepath, System.IO.FileMode.Open,System.IO.FileAccess.Read, System.IO.FileShare.Read ); 

            // Total bytes to read:
            long bytesToRead = stream.Length;
            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);
            // Read the bytes from the stream in small portions.
            while (bytesToRead > 0)
            {
                // Make sure the client is still connected.
                if (Response.IsClientConnected)
                {
                    // Read the data into the buffer and write into the
                    // output stream.
                    byte[] buffer = new Byte[10000];
                    int length = stream.Read(buffer, 0, 10000);
                    Response.OutputStream.Write(buffer, 0, length);
                    Response.Flush();
                    // We have already read some bytes.. need to read
                    // only the remaining.
                    bytesToRead = bytesToRead - length;
                }
                else
                {
                    // Get out of the loop, if user is not connected anymore..
                    bytesToRead = -1;
                }
            }
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
            // An error occurred..
        }
        finally
        {
            if (stream != null)
            {
                stream.Close();
            }
        }
    }