? sites/default/files
? sites/default/settings.php
Index: includes/file.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/file.inc,v
retrieving revision 1.137
diff -u -p -r1.137 file.inc
--- includes/file.inc	9 Oct 2008 20:07:00 -0000	1.137
+++ includes/file.inc	9 Oct 2008 22:05:00 -0000
@@ -1218,7 +1218,9 @@ function file_set_status($file, $status 
  *   An array of HTTP headers to send along with file.
  */
 function file_transfer($source, $headers) {
-  ob_end_clean();
+  if (ob_get_level()) {
+    ob_end_clean();
+  }
 
   foreach ($headers as $header) {
     // To prevent HTTP header injection, we delete new lines that are