With the major changes to Drupal with version 8, it seems I would need Drush 7.x or earlier to work with Drupal 7.x. I tried to rebuild the cache and I got errors related to namespaces in PHP. It seemed to be looking for features that were not part of Drupal 7.x.
Are there different commands to clear the cache for a Drupal 7.x site?
drush cr and it came back with errors indicating it was trying to find code using namespaces, but Drupal 7.x core doesn't use namespaces in the code.
I tried it on Ubuntu and on Windows.