And then it happened again. I could add posts before I used the WordPress Importer plugin (to re-import my old content) and then could not post comments after that.
After a month of not being able to post, I gave up, nuked the WordPress installation and started over.
This may or may not be related, but ever since this occurred two days ago, I have been unable to create new posts. I get this error:
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Are you sure you want to do this?
Please try again.
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I am having the same issue – using wordpress 3.3, and I also tried the things that Mark listed above. I also tried deleting the plugin and reinstalling it.
This really gets me because my first import was a small subset of the XML file as a test – when I tried to import the entire file, it gave me that error.