Erro ao usar uma gem

Programação Ruby on Rails
#1

Olá,

Estou tentando usar uma gem chamada annotate-models (https://github.com/ctran/annotate_models), instalada a partir do comando “gem install xxx”. Ao tentar executa-la atraves do comando annotate, a seguinte msg de erro é retornada

anderson@PC:~/railsApps/exemplo$ annotate
/usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:239:in `require': no such file to load -- annotate/annotate_models (LoadError)
	from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:239:in `require'
	from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:225:in `load_dependency'
	from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:596:in `new_constants_in'
	from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:225:in `load_dependency'
	from /usr/lib/ruby/gems/1.8/gems/activesupport-3.0.3/lib/active_support/dependencies.rb:239:in `require'
	from /usr/lib/ruby/gems/1.8/gems/annotate-2.4.0/lib/tasks/annotate_models.rake:3
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `call'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:636:in `execute'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `each'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:631:in `execute'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:597:in `invoke_with_call_chain'
	from /usr/lib/ruby/1.8/monitor.rb:242:in `synchronize'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:590:in `invoke_with_call_chain'
	from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake.rb:583:in `invoke'
	from /usr/lib/ruby/gems/1.8/gems/annotate-2.4.0/bin/annotate:67
	from /usr/bin/annotate:19:in `load'
	from /usr/bin/annotate:19

Parece se tratar de dependências, mas nao sei como resolver. Estou usando ubuntu 10.10 com ruby 1.8.7 e rails 3.0.3

Grato

#2