Rake Aborted Error when pushing to Heroku (factory_girl)

Something is still trying to load factory_girl, so I'd try running rake db:migrate --trace to see if that provides any helpful info.

Even more to the point, are your specs being compiled into your slug? If so, try including the spec dir in .slugignore. (Basically I'm guessing some unintended side effect is referencing f_g and that seems a likely culprit to me.)