As some of you have noticed, the Twitter API recently changed. While we haven't gotten around to fixing it, you can still post to Twitter! Enter: TwitterFeed
Once you sign up (it's free!) and name your feed, it will ask for your blog or RSS feed URL. For your Natuba account, it's www.natuba.com/(your username)/feed. For example, mine would be: www.natuba.com/utmark/feed
Next, you will see the services they work with. Select Twitter, and click the blue "Authenticate Twitter" button. Enter your Twitter username and password, click the "Create Service" button at the bottom of the page, then "All Done!" on the following page, and you're all set up!
There are also many advanced settings you can control, from frequency of updates to any text you want to add before and/or after your post. Enjoy!