Cannot run puma server for my application because of bcrypt - ruby-on-rails

Question

My machine is a Windows 8 32 bit machine and I have ruby 2.1.8.
I am facing a problem when I am trying to open my app in puma and rails server. I am even unable to run bundle install. The erorr is:
in `require': 126: The specified module could not be found.
- C:/Ruby21/lib/ruby/gems/2.1.0/gems/bcrypt-ruby-3.1.1.rc1-x86-mingw32/lib/bcrypt_ext.so (LoadError)
and the bundle install error is:
could not find gem 'bcrypt (=3.1.5 rc1) x64-mingw32' in any of the gemfile ruby 2.1.8
same problem happens also for bcrypt version 3.0.0 and 3.1.1 also
My Gemfile is:
source 'http://rubygems.org'
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '4.1.9'
# Use sqlite3 as the database for Active Record
gem 'pg'
gem 'plivo'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 4.0.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# Use CoffeeScript for .js.coffee assets and views
gem 'coffee-rails', '~> 4.0.0'
gem 'coffee-script-source', '1.8.0'
# See https://github.com/sstephenson/execjs#readme for more supported runtimes
# gem 'therubyracer', platforms: :ruby
# Use jquery as the JavaScript library gem 'jquery-rails'
gem 'rails-jquery-autocomplete', :git 'https://github.com/AyushRuiaHW/rails-jquery-autocomplete.git'
# Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks
gem 'turbolinks'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 1.2'
group :doc do
# bundle exec rake doc:rails generates the API under doc/api.
gem 'sdoc', require: false
end
gem 'tzinfo-data'
gem 'faraday'
gem 'hypdf', '~> 1.0.12'
gem 'currency-in-words'
gem "jquery-ui-rails"
gem 'Instamojo-rb'
gem "kaminari"
gem "rails-erd"
gem 'levenshtein', '~> 0.2.2'
gem "lol_dba"
gem "bullet", :group => "development"
gem "bootstrap-sass"
gem 'rack-mini-profiler'
gem 'newrelic_rpm'
gem 'puma_worker_killer'
# Use ActiveModel has_secure_password
# gem 'bcrypt-ruby', '~> 3.0.0'
# Use unicorn as the app server
# gem 'unicorn'
# Use Capistrano for deployment
# gem 'capistrano', group: :development
# Use debugger
# gem 'debugger', group: [:development, :test]
gem 'postmark-rails'
gem 'bcrypt-ruby', '3.1.5.rc1', :require => 'bcrypt'
gem 'puma'
gem "paperclip", "~> 3.0"
gem 'aws-sdk', '~> 1'
gem 'aws-sdk-resources', '~> 2'
gem 'rails_12factor', group: :production
ruby "2.1.8"

Answer 1

delete your old gem 'bcrypt-ruby',and insert
gem 'bcrypt', '~> 3.1', '>= 3.1.11'
and run
bundle install

Answer 2

You need to remove your old gem and update your gemfile with following
gem 'bcrypt-ruby', '~> 3.1.0'
and run bundle install , then restart your server.
You might also want to try deleting your gemfile.lock and re-running bundle install.
OR
you can install gem bcrypt directly from command line as following :
gem install --version='3.1.0' bcrypt-ruby
then run bundle install