You have gone through your regular module update routine and cleared the cache. Suddenly you are presented with a PHP Fatal error, because a class can’t be found. Your Drupal site won’t load and you can’t run Drush commands. All you get is the fatal error blocking the site.

If you get a fatal error like above where a class is not found, a likely cause is that the Drupal registry has the old path for the class. A cache clear should update, but sometimes it all goes a bit wrong. The solution is to rebuild the registry. This will update the registry table with the new file locations. Read on to find out how...