If you're using shared hosting and have multiple domains on your site (Add-on Domains in the CPANEL world), be careful about moving. Some shared hosting services put all of your files including directories for subdomains in an htdocs folder (or some other name). Others place them in a www folder. Some do both, and sometimes the documentation reflects the fact that you can choose -- or it may simply be outdated. Place an index.html file in the directory you are moving to and make certain that you can get to it before you move the Drupal files. We also discovered a gotcha. In the File System module under Site Configuration you specify two directories. The File System Path is usually sites/default/files and the Temporary path is tmp. Both are normally relative to the Drupal root -- in other words, they are directly beneath the Drupal folder. Somewhere along the line, our tmp path wound up being fully qualified--that is, it was relative to the site root, not the Drupal too. This works just fine until you move and the fully qualified path can't be found. Drupal isn't happy. Moral: check paths in your configuration to make certain that they are Drupal-root-relative so they can be moved.