Thomas O. on "[Plugin: WordPress Simple Firewall] Getting error when trying to update a Page or Post"

Using 1.5.5

I'm getting a 500 server error when I try to update a Page or Post. When I click "Update" the browser just says Server error and states:

"The website encountered an error while retrieving http://example.com/wp-admin.post.php. It may be down for maintenance or configured incorrectly."

If I deactivate the plugin, then I have no problems.

I turned on the logging, but I didn't see any useful information.

Is there anything else that I should probably look for?

http://wordpress.org/plugins/wp-simple-firewall/