Last week, to appropriate fanfares, Drupal 8 reached Release Candidate stage. That means Drupal 8 tagged releases now have an upgrade path between them, and it also means (very nearly) complete API / hook stability - which means this is the cue for some serious testing and development of contrib themes and modules.
However I made one schoolboy error: I was still using Drush 7.
It's actually quite an understandable mistake - all you had to do was follow the development of Drupal Next, and Drush, but not quite follow it closely enough. … Read more about For Drupal 8, use Drush 8