Looking for a way to post to WordPress from my iPhone, I downloaded the WordPress application.  Soon after running the app and attempting to connect to my site, I was notified that I need to enable XML-RPC remote publishing.  That being said, I went to my site and made the following changes:

If your blog runs WordPress 2.6 or later; in my case 3.1.1, you must explicitly enable the XML-RPC remote publishing interface.

[Step 1] Log in to your blog with the admin account, and go to Settings, and then Writing.

[Step 2] Check the box next to “XML-RPC” on the Writing options page, and save the settings.