MobileMe: Troubleshooting publishing from iLife applications or Aperture

Sometimes you may find that publishing to MobileMe from Aperture or iLife applications (such as iPhoto or iMovie) does not succeed. You may see error messages such as the following: "An error occurred while publishing the album <My Album>. Request to the server failed." "An error occurred while publish the album <My Album>.  This is not a valid location for this request." "Unsupported iPhoto Images...1 file will not be imported from iPhoto because the file is either an unsupported file format or a movie."