Index: fckeditor/fckeditor.module
===================================================================
--- fckeditor/fckeditor.module	(revision 4366)
+++ fckeditor/fckeditor.module	(working copy)
@@ -183,7 +183,7 @@
           // The element before this element is the target form field.
           $field = &$form[$children[$index - 1]];
           $textarea_id = $field['#id'];
-          $js_id = $_fckeditor_js_ids[$textarea_id];
+          $js_id = isset($_fckeditor_js_ids[$textarea_id]) ? $_fckeditor_js_ids[$textarea_id] : NULL;
 
           array_push($processed_textareas, $js_id);