Pages are not accessible, menu links are not displaying properly I'm trying to resurrect a Drupal 4 site which stopped working at some unknown point, possibly months ago. I can login as admin and reach the front page. Every link after that returns 'you are not authorized to access this page'. The primary_links and secondary_links menus are not being retrieved properly. I have tried switching themes and clearing the cache table. I have also set up a local version for debugging but there are no PHP errors being thrown.

I'm running php 5.2.13, mysql 5.1.44.
As I have noted in the comments of the first answer, the issue was due to a change in versions of PHP. The bug was previously reported here.