CKEditor.

The error came from some script in Application.js

public/javascripts/ckeditor/_samples/api_dialog/my_dialog.js

@@ -0,0 +1,28 @@
+/*
+Copyright (c) 2003-2011, CKSource - Frederico Knabben. All rights reserved.
+For licensing, see LICENSE.html or http://ckeditor.com/license
+*/
+
+CKEDITOR.dialog.add( 'myDialog', function( editor )
+{
+	return {
+		title : 'My Dialog',
+		minWidth : 400,
+		minHeight : 200,
+		contents : [
+			{
+				id : 'tab1',
+				label : 'First Tab',
+				title : 'First Tab',
+				elements :
+				[
+					{
+						id : 'input1',
+						type : 'text',
+						label : 'Input 1'
+					}
+				]
+			}
+		]
+	};
+} );