Redmine

When I upgrade redmine from 1.2.1 to 2.1.2 when i trying to migrate plugins i have this error every time i execute a rake command.

Please any idea about this error ?

rake --trace
rake aborted!
no such file to load -- timecop
/home/formation1/redmine-2.1/plugins/redmine_backlogs/lib/tasks/test.rake:5:in `require'
/home/formation1/redmine-2.1/plugins/redmine_backlogs/lib/tasks/test.rake:5
/home/formation1/redmine-2.1/lib/tasks/redmine.rake:121:in `load'
/home/formation1/redmine-2.1/lib/tasks/redmine.rake:121
/home/formation1/redmine-2.1/lib/tasks/redmine.rake:121:in `each'
/home/formation1/redmine-2.1/lib/tasks/redmine.rake:121
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/engine.rb:425:in `load'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/engine.rb:425:in `load_tasks'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/engine.rb:425:in `each'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/engine.rb:425:in `load_tasks'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/application.rb:145:in `load_tasks'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/railtie/configurable.rb:30:in `send'
/usr/lib/ruby/gems/1.8/gems/railties-3.2.8/lib/rails/railtie/configurable.rb:30:in `method_missing'
/home/formation1/redmine-2.1/Rakefile:7
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/rake_module.rb:25:in `load'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/rake_module.rb:25:in `load_rakefile'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:501:in `raw_load_rakefile'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:82:in `load_rakefile'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:81:in `load_rakefile'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:65:in `run'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:133:in `standard_exception_handling'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:63:in `run'
/usr/lib/ruby/gems/1.8/gems/rake-0.9.2.2/bin/rake:33
/usr/bin/rake:23:in `load'
/usr/bin/rake:23