Rake Migrate plugins error

[Laurent HADJADJ]

Hi, i have a error when a want to install teh plugins. I use a redmine (Deblan 8) 2.5.x.
I install also : gem install activerecord
Do you have any idea ?
Thanks

---

redmine# rake redmine:plugins:migrate RAILS_ENV=production
[DEPRECATION] requiring "RMagick" is deprecated. Use "rmagick" instead
rake aborted!
NameError: uninitialized constant ActiveRecord::Observer
/usr/share/redmine/plugins/redshares/lib/redshare_observer.rb:1:in <top (required)>' /usr/share/redmine/plugins/redshares/init.rb:3:in<top (required)>'
/usr/share/redmine/lib/redmine/plugin.rb:139:in block in load' /usr/share/redmine/lib/redmine/plugin.rb:130:ineach'
/usr/share/redmine/lib/redmine/plugin.rb:130:in load' /usr/share/redmine/config/initializers/30-redmine.rb:21:in<top (required)>'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/engine.rb:648:in block in load_config_initializer' /var/lib/gems/2.1.0/gems/activesupport-4.1.15/lib/active_support/notifications.rb:161:ininstrument'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/engine.rb:647:in load_config_initializer' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/engine.rb:612:inblock (2 levels) in class:Engine'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/engine.rb:611:in each' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/engine.rb:611:inblock in class:Engine'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:30:in instance_exec' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:30:inrun'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:55:in block in run_initializers' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:44:ineach'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:44:in tsort_each_child' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/initializable.rb:54:inrun_initializers'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/application.rb:300:in initialize!' /usr/share/redmine/config/environment.rb:14:in<top (required)>'
/var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/application.rb:276:in require_environment!' /var/lib/gems/2.1.0/gems/railties-4.1.15/lib/rails/application.rb:405:inblock in run_tasks_blocks'
/var/lib/gems/2.1.0/gems/rake-11.2.2/exe/rake:27:in `<top (required)>'
Tasks: TOP => redmine:plugins:migrate => environment
(See full trace by running task with --trace)