If you're using a subfolder in htdocs then make sure your rewrite base reflects this.
Thanks. It was sending me to index when it ran into an error. My problem was not appending .html. If I change the documents to containers, they work without the html, but I'm not sure whether that's best practice.
Ah ok
If you go to content types in your manager (manager/?a=system/contenttype) and just remove the .html extension value then they'll work without needing to stick the extension on the end of the url.