Index: file.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/file/file.module,v
retrieving revision 1.50
diff -u -p -r1.50 file.module
--- file.module	29 Dec 2010 04:35:23 -0000	1.50
+++ file.module	2 Jan 2011 01:39:03 -0000
@@ -533,8 +533,8 @@ function file_managed_file_validate(&$el
   // If referencing an existing file, only allow if there are existing
   // references. This prevents unmanaged files from being deleted if this
   // item were to be deleted.
-  $clicked_button = end($form_state['clicked_button']['#parents']);
-  if ($clicked_button != 'remove_button' && !empty($element['fid']['#value'])) {
+  $triggering_element = end($form_state['triggering_element']['#parents']);
+  if ($triggering_element != 'remove_button' && !empty($element['fid']['#value'])) {
     if ($file = file_load($element['fid']['#value'])) {
       if ($file->status == FILE_STATUS_PERMANENT) {
         $references = file_usage_list($file);
@@ -549,7 +549,7 @@ function file_managed_file_validate(&$el
   }
 
   // Check required property based on the FID.
-  if ($element['#required'] && empty($element['fid']['#value']) && !in_array($clicked_button, array('upload_button', 'remove_button'))) {
+  if ($element['#required'] && empty($element['fid']['#value']) && !in_array($triggering_element, array('upload_button', 'remove_button'))) {
     form_error($element['upload'], t('!name field is required.', array('!name' => $element['#title'])));
   }