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 checked the page source and all of the header information is intact, the CSS links, meta information, javascripts, etc., but it stop before the closing head tag and there's nothing else after that.
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?