Trying to redirect after filedownload

Hi, I am trying to redirect the user to a clean node after downloading a file to the user. It works but is producing the normal pre-empted header error in the watchdog log:

warning: Cannot modify header information - headers already sent by (output started at /home/james/public_html/drupal/modules/webform/webform.inc

Here is the code fragment:

  ...
  $title_string = $node_info->title;
  $file_name = _webform_print_csv_string($title_string,arg(2),'file');

  drupal_set_header("Content-type: text/html; charset=utf-8");
  drupal_set_header("Content-Disposition: attachment; filename=" . $title_string . ".csv");

  @readfile($file_name);

  drupal_goto("webform");		// and back to the start
  ...

How should this be done? As I say, it is working as far as the user is concerned, but producing the watchdog error entry.
I tried a few interdictory lines, ie: //while (@ob_end_flush()); // No avail !!