Index: modules/node/content_types.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/node/content_types.inc,v
retrieving revision 1.24.2.3
diff -u -p -r1.24.2.3 content_types.inc
--- modules/node/content_types.inc	27 Dec 2007 09:57:47 -0000	1.24.2.3
+++ modules/node/content_types.inc	27 Jan 2008 19:19:58 -0000
@@ -236,9 +236,11 @@ function node_type_form_validate($form_i
     if (!preg_match('!^[a-z0-9_]+$!', $type->type)) {
       form_set_error('type', t('The machine-readable name can only consist of lowercase letters, underscores, and numbers.'));
     }
-    // The type cannot be just the character '0', since elsewhere we check it using empty().
-    if ($type->type === '0') {
-      form_set_error('type', t("Invalid type. Please enter a type name other than '0' (the character zero)."));
+    // 'theme' conflicts with theme_node_form()
+    // 'add' and 'list' conflict with menu paths
+    // '0' is invalid, since elsewhere we check it using empty().
+    if (in_array($type->type, array('0', 'theme', 'add', 'list'))) {
+      form_set_error('type', t("Invalid machine-readable name. Please enter a name other than %invalid.", array('%invalid' => $type->type)));
     }
   }