Thread:Project:Support desk/Fatal Error while upgrading from 1.16.5 to 1.17

After upgrading my wiki from MW 1.16.5 to 1.17 (release 1.17.0) I get this: Fatal error: Call to a member function setCacheTime on a non-object in (path-to-wiki)/includes/parser/Parser.php on line 4771 when I open a special page that doesn't refer to the database or run update.php. What can it be&