Came across this error when trying out the ruby on rails tutorial section with rspec on a windows platform using jruby 1.6:
c:\\rails_projects\\sample_app>
I had the same problem but for a different reason:
in my spork.prefork block within my spec_helper.rb file I had this line
Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}
but within one of the files that was being required above (spec/support/some_helper_file.rb) was a require 'spec_helper' call
removing this unneeded require solved the issue