forum.module comes with a built-in menu link that is placed into the menu Navigation. If I try to move this menu link to the main Main menu, I get the following error:Notice: Undefined index: localized_options in menu_navigation_links() (line 1860
This problem was first identified on Drupal installed on a windows host. It may exist on other platforms as well.
Work-around solution: Disable the link in Navigation and create a new link for the Main menu.