I'm using a more or less fresh local install of WP 3.3.1. A few days ago I set up a couple menus (Appearance > Menus) without a hitch. Today I tried creating a new menu and add a page to it, but the page was never successfully added to the menu; the spinner just went on forever.
I thought maybe the menu name was conflicting with one I had deleted earlier, but I can no longer add pages to new or existing menus. The same goes for custom links; I just get the spinner even after waiting 15 minutes.
I only have one plugin enabled, Advanced Custom Fields 3.0.6, which I disabled to no avail. I have no custom post types or taxonomies. There are about 15 pages total with very little content on them, so WP isn't getting stuck sifting through a bunch of data. Any other ideas?