Rails - Jun 2005 - problem with rails rails-0.12.1 with Ruby 1.8 on OS X Panther

I have installed ruby, gem and rails.
I am trying to create a new project and I get some error messages.
undefined method `write_inheritable_attribute'' for
Rails::Generator::Base:Class (NoMethodError)

Am I missing something?

regards,

Arnaud

PS: detail of the error message I get.

$ ruby /usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/rails
/usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/../lib/rails_generator/options.rb:33:in
`default_options'': undefined method
`write_inheritable_attribute'' for
Rails::Generator::Base:Class (NoMethodError)
        from
/usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/../lib/rails_generator/base.rb:51
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:18:in
`require__''
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:18:in
`require''
        from
/usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/../lib/rails_generator.rb:34
        from /usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/rails:3:in
`require''
        from /usr/local/lib/ruby/gems/1.8/gems/rails-0.12.1/bin/rails:3

-- 
Arnaud Sahuguet