Index: modules/node/content_types.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/node/content_types.inc,v
retrieving revision 1.49
diff -u -p -r1.49 content_types.inc
--- modules/node/content_types.inc	22 Dec 2007 23:24:25 -0000	1.49
+++ modules/node/content_types.inc	4 Jan 2008 00:37:09 -0000
@@ -234,8 +234,10 @@ function node_type_form_validate($form, 
       form_set_error('type', t('The machine-readable name must contain only lowercase letters, numbers, and underscores.'));
     }
     // The type cannot be just the character '0', since elsewhere we check it using empty().
-    if ($type->type === '0') {
-      form_set_error('type', t("Invalid type. Please enter a type name other than '0' (the character zero)."));
+    foreach(array('add', 'list', '0') as $invalid) {
+      if ($type->type === $invalid) {
+        form_set_error('type', t("Invalid type. Please enter a type name other than '!invalid'.", array('!invalid' => $invalid)));
+      }
     }
   }