WordPress Partner

The three most common reasons for not being able to access robot.txt are:

In WordPress, "I would like my blog to be visible to everyone" isn’t selected  (it’s on "privacy" under configurations)

There are no Posts in your WordPress (if you delete all Posts i.e. only have pages, the virtual robots.txt isn’t created)

You have a static robots.txt in the root of your domain (a static robots.txt overrides the virtual robots.txt)

Are there WordPress Plugins to create a robots.txt file?

Yes there are numerous Plugins that will help to either manipulate the virtual robots.txt or create a static robots.txt (remember that the virtual robots.txt will not work if a physical robots.txt exists in the URL root).

Related posts:

1. How do I add to WordPress robots.txt?
2. What is a virtual Robots.txt?
3. What is robots.txt?