Today Rails 2.3 was pushed. Upgrading some applications created a couple of issues.
NameError (uninitialized constant ApplicationController)
In previous versions of Rails, the generator would create application.rb for the Application Controller. In 2.3 the file is now properly named application_controller.rb.
NameError (uninitialized constant ActionController::Caching::Sweeper)
This is a bug that is part of the 2.3 release. The fix is was supposedly resolved according to this ticket previous to 2.3 but something is still off.