私は昨日からこの問題で立ち往生しており、インターネットを精査しましたが、「rails generate devise User」を実行した後に多くの人が同じエラーを経験しているようです
Devise の最新バージョン (3.0.0.rc) と思われるものを実行していますが、「rails server」を実行しようとすると、以下のエラー メッセージが表示されます。（インストール時にdeviseから与えられた指示に従いました）
モデルを破棄できず、データベースを移行できず、プロジェクト全体を削除して毎回やり直す必要があります。
助けてください！
C:\Sites\blogbar>rails server
=> Booting WEBrick
=> Rails 4.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-4.0.0/lib/act
ive_support/dependencies.rb:228:in `require': cannot load such file -- 1.9/bcryp
t_ext (LoadError)
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `block in require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `block in load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:615:in `new_constants_in'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/bcrypt-ruby-3.
1.0-x86-mingw32/lib/bcrypt_ext.rb:2:in `<top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `block in require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `block in load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:615:in `new_constants_in'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/bcrypt-ruby-3.
1.0-x86-mingw32/lib/bcrypt.rb:12:in `<top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `block in require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `block in load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:615:in `new_constants_in'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:211:in `load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models/database_authenticatable.rb:2:in `<top (required
)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:97:in `const_get'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:97:in `block (2 levels) in devise'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:92:in `each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:92:in `block in devise'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:123:in `devise_modules_hook!'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/models.rb:90:in `devise'
from C:/Sites/blogbar/app/models/user.rb:5:in `<class:User>'
from C:/Sites/blogbar/app/models/user.rb:1:in `<top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:423:in `load'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:423:in `block in load_file'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:615:in `new_constants_in'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:422:in `load_file'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:323:in `require_or_load'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:462:in `load_missing_constant'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:183:in `const_missing'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/inflector/methods.rb:226:in `const_get'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/inflector/methods.rb:226:in `block in constantize'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/inflector/methods.rb:224:in `each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/inflector/methods.rb:224:in `inject'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/inflector/methods.rb:224:in `constantize'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:534:in `get'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:565:in `constantize'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise.rb:274:in `get'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/mapping.rb:77:in `to'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/mapping.rb:72:in `modules'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/mapping.rb:89:in `routes'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/mapping.rb:156:in `default_used_route'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/mapping.rb:66:in `initialize'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise.rb:308:in `new'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise.rb:308:in `add_mapping'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/rails/routes.rb:208:in `block in devise_for'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/rails/routes.rb:207:in `each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/bundler/gems/devise
-3c519b13ff94/lib/devise/rails/routes.rb:207:in `devise_for'
from C:/Sites/blogbar/config/routes.rb:3:in `block in <top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/actionpack-4.0
.0/lib/action_dispatch/routing/route_set.rb:316:in `instance_exec'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/actionpack-4.0
.0/lib/action_dispatch/routing/route_set.rb:316:in `eval_block'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/actionpack-4.0
.0/lib/action_dispatch/routing/route_set.rb:294:in `draw'
from C:/Sites/blogbar/config/routes.rb:1:in `<top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:222:in `load'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:222:in `block in load'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:213:in `load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:222:in `load'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:40:in `block in load_paths'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:40:in `each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:40:in `load_paths'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:16:in `reload!'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:26:in `block in updater'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/file_update_checker.rb:75:in `call'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/file_update_checker.rb:75:in `execute'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/routes_reloader.rb:27:in `updater'
from C:65535:in `execute_if_updated'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application/finisher.rb:69:in `block in <module:Finisher>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/initializable.rb:30:in `instance_exec'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/initializable.rb:30:in `run'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/initializable.rb:55:in `block in run_initializers'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:150:in `block i
n tsort_each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:183:in `block (
2 levels) in each_strongly_connected_component'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:219:in `each_st
rongly_connected_component_from'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:182:in `block i
n each_strongly_connected_component'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:180:in `each'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:180:in `each_st
rongly_connected_component'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/tsort.rb:148:in `tsort_e
ach'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/initializable.rb:54:in `run_initializers'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/application.rb:215:in `initialize!'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/railtie/configurable.rb:30:in `method_missing'
from C:/Sites/blogbar/config/environment.rb:5:in `<top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `block in require'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:213:in `load_dependency'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/activesupport-
4.0.0/lib/active_support/dependencies.rb:228:in `require'
from C:/Sites/blogbar/config.ru:3:in `block in <main>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/builder.rb:55:in `instance_eval'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/builder.rb:55:in `initialize'
from C:/Sites/blogbar/config.ru:in `new'
from C:/Sites/blogbar/config.ru:in `<main>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/builder.rb:49:in `eval'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/builder.rb:49:in `new_from_string'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/builder.rb:40:in `parse_file'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/server.rb:277:in `build_app_and_options_from_config'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/server.rb:199:in `app'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/commands/server.rb:48:in `app'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/rack-1.5.2/lib
/rack/server.rb:314:in `wrapped_app'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/commands/server.rb:75:in `start'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/commands.rb:78:in `block in <top (required)>'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/commands.rb:73:in `tap'
from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/railties-4.0.0
/lib/rails/commands.rb:73:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'