Redmine

Hello,

Newbie in Redmine, Rails and Ruby, i installed a Squeeze 6, Redmine-Turnkey appliance in VirtualBox
and tried to install "Users XLS import/export Plugin"
I installed :

• spreadsheet gem
• redmine_plugin_views_revisions
• redmine_users_xls_impex

I have two problems :

• Plugin assets directory writable : Warning. -> How to FIX this ?
• Import and Export links in "Aministration", "Users Page" fail with message page :
  Redmine 500 Error
Internal error
An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.
If you are the Redmine administrator, check your log files for details about the error.

Perhaps, i missed something in installation ? Below are informations on my installation (configuration, production.log, ...)
Could you help me ?
Thanks

My configuration (Information page)
Informations
Warning : Plugin assets directory writable
Environment:
Redmine version 2.2.3.stable
Ruby version 1.8.7 (x86_64-linux)
Rails version 3.2.12
Environment production
Database adapter MySQL
Redmine plugins:
redmine_plugin_views_revisions 0.0.1
redmine_users_xls_impex 0.1.1

Installation procedure
gem install spreadsheet
plugin views_revisions directory in /var/wwwredmine/plugins
rake redmine:plugins:migrate RAILS_ENV=production
plugin redmine_users_xls_impex directory in /var/wwwredmine/plugins
rake redmine:plugins:migrate RAILS_ENV=production
rake redmine:plugins:process_version_change RAILS_ENV=production
/etc/init.d/apache2 restart

Production.log
@
Started GET "/users" for 192.168.0.10 at Mon Sep 23 22:52:25 +0000 2013
Processing by UsersController#index as HTML
Current user: admin (id=1)
Rendered plugins/redmine_users_xls_impex/app/views/users/index.html.erb within layouts/admin (33.2ms)
Rendered admin/_menu.html.erb (15.1ms)
Rendered layouts/base.html.erb (28.2ms)
Completed 200 OK in 98ms (Views: 78.6ms | ActiveRecord: 4.1ms)
Started GET "/users_xls_impex/import_start" for 192.168.0.10 at Mon Sep 23 22:52:35 +0000 2013

LoadError (no such file to load -- spreadsheet):
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
activesupport (3.2.12) lib/active_support/dependencies.rb:236:in `load_dependency'
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
plugins/redmine_users_xls_impex/app/controllers/users_xls_impex_controller.rb:1
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
activesupport (3.2.12) lib/active_support/dependencies.rb:236:in `load_dependency'
activesupport (3.2.12) lib/active_support/dependencies.rb:251:in `require'
activesupport (3.2.12) lib/active_support/dependencies.rb:359:in `require_or_load'
activesupport (3.2.12) lib/active_support/dependencies.rb:502:in `load_missing_constant'
activesupport (3.2.12) lib/active_support/dependencies.rb:192:in `const_missing'
activesupport (3.2.12) lib/active_support/dependencies.rb:190:in `each'
activesupport (3.2.12) lib/active_support/dependencies.rb:190:in `const_missing'
activesupport (3.2.12) lib/active_support/inflector/methods.rb:219:in `constantize'
activesupport (3.2.12) lib/active_support/inflector/methods.rb:218:in `each'
activesupport (3.2.12) lib/active_support/inflector/methods.rb:218:in `constantize'
activesupport (3.2.12) lib/active_support/dependencies.rb:554:in `get'
actionpack (3.2.12) lib/action_dispatch/routing/route_set.rb:69:in `controller_reference'
actionpack (3.2.12) lib/action_dispatch/routing/route_set.rb:54:in `controller'
actionpack (3.2.12) lib/action_dispatch/routing/route_set.rb:32:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.12) lib/action_dispatch/routing/route_set.rb:601:in `call'
rack-openid (1.3.1) lib/rack/openid.rb:98:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.5) lib/rack/etag.rb:23:in `call'
rack (1.4.5) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context'
rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/cookies.rb:341:in `call'
activerecord (3.2.12) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.12) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/callbacks.rb:28:in `call'
activesupport (3.2.12) lib/active_support/callbacks.rb:405:in `_run__235047818__call__4__callbacks'
activesupport (3.2.12) lib/active_support/callbacks.rb:405:in `send'
activesupport (3.2.12) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.12) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.12) lib/active_support/callbacks.rb:81:in `send'
activesupport (3.2.12) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.12) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.12) lib/rails/rack/logger.rb:32:in `call_app'
railties (3.2.12) lib/rails/rack/logger.rb:16:in `call'
activesupport (3.2.12) lib/active_support/tagged_logging.rb:22:in `tagged'
railties (3.2.12) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.5) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.12) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.5) lib/rack/lock.rb:15:in `call'
actionpack (3.2.12) lib/action_dispatch/middleware/static.rb:62:in `call'
rack-cache (1.2) lib/rack/cache/context.rb:136:in `forward'
rack-cache (1.2) lib/rack/cache/context.rb:245:in `fetch'
rack-cache (1.2) lib/rack/cache/context.rb:185:in `lookup'
rack-cache (1.2) lib/rack/cache/context.rb:66:in `call!'
rack-cache (1.2) lib/rack/cache/context.rb:51:in `call'
railties (3.2.12) lib/rails/engine.rb:479:in `call'
railties (3.2.12) lib/rails/application.rb:223:in `call'
railties (3.2.12) lib/rails/railtie/configurable.rb:30:in `send'
railties (3.2.12) lib/rails/railtie/configurable.rb:30:in `method_missing'
passenger (3.0.19) lib/phusion_passenger/rack/request_handler.rb:96:in `process_request'
passenger (3.0.19) lib/phusion_passenger/abstract_request_handler.rb:516:in `accept_and_process_next_request'
passenger (3.0.19) lib/phusion_passenger/abstract_request_handler.rb:274:in `main_loop'
passenger (3.0.19) lib/phusion_passenger/rack/application_spawner.rb:206:in `start_request_handler'
passenger (3.0.19) lib/phusion_passenger/rack/application_spawner.rb:171:in `send'
passenger (3.0.19) lib/phusion_passenger/rack/application_spawner.rb:171:in `handle_spawn_application'
passenger (3.0.19) lib/phusion_passenger/utils.rb:470:in `safe_fork'
passenger (3.0.19) lib/phusion_passenger/rack/application_spawner.rb:166:in `handle_spawn_application'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:357:in `__send__'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:180:in `start'
passenger (3.0.19) lib/phusion_passenger/rack/application_spawner.rb:129:in `start'
passenger (3.0.19) lib/phusion_passenger/spawn_manager.rb:253:in `spawn_rack_application'
passenger (3.0.19) lib/phusion_passenger/abstract_server_collection.rb:132:in `lookup_or_add'
passenger (3.0.19) lib/phusion_passenger/spawn_manager.rb:246:in `spawn_rack_application'
passenger (3.0.19) lib/phusion_passenger/abstract_server_collection.rb:82:in `synchronize'
passenger (3.0.19) lib/phusion_passenger/abstract_server_collection.rb:79:in `synchronize'
passenger (3.0.19) lib/phusion_passenger/spawn_manager.rb:244:in `spawn_rack_application'
passenger (3.0.19) lib/phusion_passenger/spawn_manager.rb:137:in `spawn_application'
passenger (3.0.19) lib/phusion_passenger/spawn_manager.rb:275:in `handle_spawn_application'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:357:in `__send__'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:357:in `server_main_loop'
passenger (3.0.19) lib/phusion_passenger/abstract_server.rb:206:in `start_synchronously'
passenger (3.0.19) helper-scripts/passenger-spawn-server:99@