I recently upgraded from 2.0.4 to 2.2.1, and now all the AJAX-related WordPress admin functions don't work. These include autosave, deleting comments, and adding categories. Might also be true for deleting posts but I don't want to risk trying.
I tried reinstalling WordPress completely, but the issue remains. I've read a few other threads about similar problems, but I don't get an error message about permissions like most people do. I get the main admin page loaded into the page element that is supposed to receive the ajax response. Here's a screenshot of a failed autosave.
I tried the fix at...
but that didn't change anything. Any ideas?