Rake 0.9.2, Rails 3.0.8 rc1: undefined method `prerequisites' for nil:NilClass
run rake db:migrate error
Rails 3.1 and Rspec-rails < 2.6 isn't compatible: https://github.com/rspec/rspec-rails/blob/master/features/RailsVersions.md.
upgrade to rspec-rails version 2.6.1.beta1 fixed it.
solution:
If you haven't specified a version for rspec-rails in your Gemfile, just run bundle update.
If you have, upgrade it to 2.6.1 and run bundle update.
If you have, upgrade it to 2.6.1 and run bundle update.
something special