In lib/adminlib.php

this (at line 3517ish)...

/**

• Enrolment manage page
  */
  class admin_enrolment_page extends admin_externalpage {
  public function admin_enrolment_page() { global $CFG; parent::admin_externalpage('enrolment', get_string('enrolments'), $CFG->wwwroot . '/'.$CFG->admin.'/enrol.php'); }

That will break on PHP4. We haven't gone to PHP5 for 1.9 have we?