CSS was not working on Heroku

Add CSS to Heroku
To load the css and assets I ran:

$ bundle exec rake assets:precompile

That still didn't work so I ran:

$ RAILS_ENV=production bundle exec rake assets:precompile

The response:

rake aborted!  
Devise.secret_key was not set. Please add the following to your Devise initializer:
config.secret_key = (gave me a long number)

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It is still not working 12-19-2015 on Linux but it works on Mac

(skeleton works on both)