I’ve redone my site (incava.org) in Rails, and do my development under 2.2. When deploying my site onto a server running Rails 2.3, there was an error:
uninitialized constant ApplicationController
After some head-scratching, I found this, which explains the error as resulting from Rails 2.3 expecting the ApplicationController class to be in app/application_controller.rb, not, as in Rails 2.2, as app/application.rb.
I took the easy approach – also maintainable under both 2.2 and 2.3 – and simply linked application_controller.rb to application.rb, which solved the problem.