In a Ruby on Rails project, when I tried to create a Devise user via FactoryGirl in a rake task, I got an error and it crashed.

■ Error Message

Could not find a valid mapping for #
And then rake, rails s, rails c - nothing worked anymore.
For now, since I was using rvm, I was able to run rake and rails s by recreating the gemset.
However, I still haven’t solved the User registration issue. Someone please help.
【Reference】
・Reloading Factory Girl Factories in the Rails 3 Console | Transcending Frontiers
・devise - “Could not find a valid mapping for #<User …>” only on second and successive tests - Stack Overflow
That’s all from the Gemba.