write > page error after upgrade to 2.3.1

I just has an uneventful upgrade to 2.3.1, but then I discover that I can’t create new pages because there’s an error

Fatal error: Call to undefined function: get_page_templates() in /home/24396/domains/XYZ.XXX/html/wp-admin/edit-page-form.php on line 88

I couldn’t find any answers in the docs/forums. I’ve re-uploaded the 2.3.1 pages for the admin AND disabled all plugins with no luck. Anyone got an answer? I used this same code with no issues (downloaded yesterday, installed on 2 other blogs).