error loading autotest (can't activate builder)

$ autotest
loading autotest/cucumber_rails_rspec2
Error loading Autotest style autotest/cucumber_rails_rspec2 (can't activate builder (~> 
2.1.2, runtime) for ["activemodel-3.0.6", "actionpack-3.0.6", "rspec-rails-2.5.0"], 
already activated builder-3.0.0 for [开发者_开发百科"cucumber-0.10.0"]). Aborting.

Any idea how to solve this? I'been trying for a while with no luck.

I'm not sure what causes that error message, but you might try running:

bundle exec autotest

this fixed a different error I had using autotest