I've seen a lot of posts that are similar to this one, but they all seem to be different at the core of the problem. So here we go:
I have a fresh WP 2.3.2 install (no upgrades or anything fancy), all plugins disabled,
using a theme of my own, which is pretty elementary.
I've added a couple of (nested) categories in the categories admin panel.
Then I go to Manage->Posts and Edit the "Hello World" post. I try to add
a category to it by checking the corresponding check box and clicking Add
(on the upper-right dialog box for Categories). Then I get the infamous
"Something strange happened message ..."
Any help, greatly appreciated.