capistrano aborts - SSHKit::Runner::ExecuteError and Devise.secret_key was not set

Question

I'm trying to update an app (Rails 4.1.12; ruby 1.9.3p484) by deploying changes from development to production using capistrano. Below is log (I masked the IP address and suggested secret key).

Previously never had a problem running a deploy. Have searched and found posts with similar errors but have not found a solution. I did follow the instructions to add Devise.secret_key to the Devise initializer and restarted the application (dev and prod). Next attempt to deploy received same error with suggestion for different secret key.

All help, hints, suggestions are greatly appreciated. Thanks.

UPDATE:I just tried to deploy using bundle exec cap production deploy and did not get errors but still get errors when running cap production deploy

UPDATE 2: I used Figaro to generate an application.yml file (and append to gitignore). In the devise.rb file I created a line config.secret_key = ENV["config.secret_key"] In the application.yml file I created a line config.secret_key: 'random_128_chr_string' I then restarted the development server and ran cap production deploy Unfortunately got same error.

cap production deploy
.
.
.
[deploy:migrate] Run `rake db:migrate`
[e0c2c251] Running bundle exec rake db:migrate as [email protected]
(Backtrace restricted to imported tasks)
cap aborted!
SSHKit::Runner::ExecuteError: Exception while executing as [email protected]: rake exit status: 1
rake stdout: Nothing written
rake stderr: rake aborted!
Devise.secret_key was not set. Please add the following to your Devise initializer:
config.secret_key = 'looong_string_of_numbers_and_letters'
Please ensure you restarted your application after installing Devise or setting the key. 

deploy.rb:

lock '>=3.2.1'

set :application, 'pepperslice'
set :repo_url, '[email protected]:jeffaltman/pepperslice.git'
set :linked_dirs, %w{log tmp public/images/uploaded}
set :linked_files, %w{config/database.yml config/initializers/devise.rb config/initializers/smtp_settings.rb}

set :format, :pretty
set :log_level, :info

namespace :deploy do

  desc 'Restart application'
  task :restart do
    on roles(:app), in: :sequence, wait: 5 do
      execute "sudo /usr/sbin/service unicorn restart"
    end
  end

  after :publishing, :restart

  after :restart, :clear_cache do
    on roles(:web), in: :groups, limit: 3, wait: 10 do
      # Here we can do anything such as:
      # within release_path do
      #   execute :rake, 'cache:clear'
      # end
    end
  end
end

capfile:

# Load DSL and Setup Up Stages
require 'capistrano/setup'

# Includes default deployment tasks
require 'capistrano/deploy'

# Includes tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
#   https://github.com/capistrano/rvm
#   https://github.com/capistrano/rbenv
#   https://github.com/capistrano/chruby
#   https://github.com/capistrano/bundler
#   https://github.com/capistrano/rails
#
# require 'capistrano/rvm'
# require 'capistrano/rbenv'
# require 'capistrano/chruby'
require 'capistrano/bundler'
# require 'capistrano/rails/assets'
require 'capistrano/rails/migrations'
#require 'capistrano/ssh_doctor'
# Loads custom tasks from `lib/capistrano/tasks' if you have any defined.
Dir.glob('lib/capistrano/tasks/*.rake').each { |r| import r }