If you checked out the Rails 3 beta recently and tried running a rake task after generating your app, there is a probably a good chance you came across the following at your command prompt:
undefined method `setup' for Bundler:Module
Hmm, oh yes, I know exactly what the problem is (not really). I was scratching my head for a bit on this one, I thought I must be missing something. After some investigation and trial and error it turns out it’s rather simple to fix. All that needs to be done is uninstall all other versions of the Bundler gem not required by the Rails 3 beta gem and the problem is solved.