Dreamhost + Rails = Explode

You have already activated rack 1.2.1, but your Gemfile requires rack 1.2.3.

gem 'rack', '1.2.1' # add this to Gemfile

The problem with this error, is that even though you've fixed the Gemfile, you've accidentally installed rack-1.2.3 by triggering this error! So we need to track down that update and delete it.

1. goto ~/.gems/gems/ on your server
2. delete rack-1.2.3

The application has exited during startup (i.e. during the evaluation of config/environment.rb).

1. delete Gemfile.lock
2. rebuild it (use bundle install)