The "migration" entity type does not exist." error after switching site file structure I am working on D6->D8 migration. We initially stared the site out using the [drupal-project](https://github.com/drupal-composer/drupal-project template), and I had my migration working. However, the site is hosted on Acquia, and Acquia requires a different file structure, so to get started, I spun up a D8 site on the Acquia free tier, and cloned that repo to my local. I got all my contrib modules and themes installed via Composer, and installed our custom modules, including my migration module. However, I am unable to bring up my site or even run a drush command (including trying to uninstall/install my migration module) because I get the following error:

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "migration" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager-&gt;getDefinition() (line 133 of core/lib/Drupal/Core/Entity/EntityTypeManager.php).


I have removed the migration configuration records from the config table and run a cache rebuild, but to no avail. I've also tried to run the drush migrate-upgrade --configure-only command, but I get this error:

Argument 3 passed to migrate_plus_migrate_prepare_row() must be an instance of Drupal\migrate\Entity\MigrationInterface, instance of    [error]
Drupal\migrate\Plugin\Migration given migrate_plus.module:66


How do I get around this?

Thanks.
The proof is in your last error message, it was expecting an Entity but it is now getting a Plugin. Migrate changed from using Config Entities to Plugins in Drupal 8.1.x so I'm presuming you've somehow triggered an upgrade.

See the change record: https://www.drupal.org/node/2668742