So I've set up a WordPress site using the Thematic framework and it's been going great for a few months now. But today I logged in and went to Appearance > Menus to change the nav menu, and I got a blank page. I tried refreshing and using a different browser to no avail. All the other Admin links work as expected.
I was thinking that it might help if I replaced the nav-menu.php file, but it didn't have any effect. Any ideas what could be going on?