I updated a WordPress blog (not my own) from version 2.1 to 2.5.1. Once done, everything else seems to work fine but children pages do not work anymore.
If I go to the url of a child page, content of its parent is shown instead. There are three parent pages with children and the same happens in all of them. If a child status of a page is removed and it has no parent the content is showing up properly. But if the page is moved back under a parent page, it does not work anymore.
How could I fix this and make the children pages work again?