The patch this page references has been closed and is now included in Drupal 6.24+.
If you have built your Drupal site on a development machine using multi-site configuration, you've discovered that there's a headache that will occur once you've ported your site to its live box. If you are about to do this, then you'll soon see the problem.
The problem lays within the site/files directory. Once you've uploaded your development site to its live server, you'll discover that you have to go into your tables and change the paths for images and other files. On your development box, you named, just for the sake of example, your site: drupal/sites/mygreatwebsite.com And in both of these directories, you've added a files directory.
To the world, that site will be: thegreatestwebsite.com and its file structure is drupal/sites/thegreatestwebsite.com Once you went live, you'll see that the paths to your images, pdf and other files looks something like this: http://thegreatestwebsite.com/sites/thegreatestwebsite.com/files/myimage...
On one hand, you gulp at the length of that url. Next, you sigh because you realize that you have to change the path -- in the database.
Drupal 7 has a fix for this -- not the length (that's another story) but for the path problem.