? sites/default/files
? sites/default/settings.php
Index: includes/form.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/form.inc,v
retrieving revision 1.297
diff -u -p -r1.297 form.inc
--- includes/form.inc	15 Oct 2008 14:17:26 -0000	1.297
+++ includes/form.inc	26 Oct 2008 15:26:29 -0000
@@ -852,7 +852,7 @@ function form_error(&$element, $message 
  *   $_POST data.
  */
 function form_builder($form_id, $form, &$form_state) {
-  static $complete_form, $cache;
+  static $complete_form, $cache, $enctype;
 
   // Initialize as unprocessed.
   $form['#processed'] = FALSE;
@@ -943,9 +943,23 @@ function form_builder($form_id, $form, &
   if (!empty($form['#cache'])) {
     $cache = $form['#cache'];
   }
-  // We are on the top form, we can copy back #cache if it's set.
-  if (isset($form['#type']) && $form['#type'] == 'form' && isset($cache)) {
-    $form['#cache'] = TRUE;
+
+  // If an element requires to set the forms content type enctype attribute, we
+  // need to store this info in a static $enctype flag to update the parent
+  // form element. E.g. For files, non-ASCII data, and binary data.
+  if (isset($form['#enctype'])) {
+    $enctype = $form['#enctype'];
+  }
+  // We are on the top form, we can copy back #cache if it's set, and set the
+  // required enctype as required.
+  if (isset($form['#type']) && $form['#type'] == 'form') {
+    if (isset($cache)) {
+      $form['#cache'] = TRUE;
+    }
+    // If there is a file element, we set the form encoding.
+    if (isset($enctype)) {
+      $form['#attributes']['enctype'] = $enctype;
+    }
   }
   return $form;
 }
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.632
diff -u -p -r1.632 system.module
--- modules/system/system.module	14 Oct 2008 20:44:57 -0000	1.632
+++ modules/system/system.module	26 Oct 2008 15:23:57 -0000
@@ -309,6 +309,7 @@ function system_elements() {
   $type['file'] = array(
     '#input' => TRUE,
     '#size' => 60,
+    '#enctype' => 'multipart/form-data',
   );