Had a weird one today: Set up a Joomla article that had "mechanical-worksheet" in the URL, like this:
http://something.com/worksheets/mechanical-worksheet
but I kept getting a 406 Not Acceptable error. A bit of searching, and it turns out that mod_security is matching the "mech" pattern and preventing the page from being served.
Got around the issue by changing the URL to ...mcncl-worksheet, but I'm curious to learn if this can be fixed more elegantly with .htaccess? I'd rather not change mod_security to allow "mech."