In trying to post about my modified Twitter stats script, I ran into a 403 Forbidden error every time I tried to publish. I could write and publish test posts with minimal text, but I could not post what I had written about my scripts.
At first I thought it was an outdated version of Wordpress that was responsible for the error. However, upgrading to 2.3 did not fix anything. I simply ignored the error and conceded that I would not be able to post anything for now.
It seems that Wordpress has some parsing issues when posts contain certain PHP commands. Apparently, modifying the mod_security rules in .htaccess helps to resolve this issue.
Adding the following code to the .htaccess file in
wp-admin/ does the trick.
<IfModule mod_security.c> SecFilterEngine Off </IfModule>