FFR: The database preferences for locally hosted Drupal sites running in Acquia Dev Desktop are located in the .acquia/DevDesktop/DrupalSettings folder in your home directory. On Widnows that’s /Users/YourName/. This is especially important if you’ve just imported a Drupal site from elsewhere that has it’s own settings.php that will be left in the structure but ignored. Things like db table prefixes are not picked up in the import process and you’re on your own to track things down to make the site run locally.
The 6th incarnation of Elmer's blog