If you are familiar with the Drupal Redirect module, you know it can be a convenient way of creating redirects from URLs that don't really exist. For example, you can create a redirect for yoursite.com/music to redirect to another website dedicated to your favorite music.
But what if the URL you want to use as a redirect does already exist? What if you want yoursite.com/testfolder to redirect to drupal.org? It won't work--you will get an error message. If you have already created a folder called testfolder, as in the image below, then your redirect won't work.