You might run into this problem if you are bringing a Rails 2.3 app onto Bundler, specifically, when you try and run “rake cucumber” or just “rake” for RSpec you get an error about uninitialized constant Rails::Boot::Bundler.

The situation is most likely that (like me) you put the preinitializer.rb file into the config/initializers directory instead of just in the config/ directory.

So double check the location as per the bundler guide