NameError: uninitialized constant I18n

Just installed the plugin as described on the link below.

If i fire up my console and then:

I18n.default_locale = “en”

i got the error message:

NameError: uninitialized constant I18n
from
/Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/active_support/dependencies.rb:278:in
load_missing_constant' from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/active_support/dependencies.rb:467:in const_missing’
from
/Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/active_support/dependencies.rb:479:in
`const_missing’
from (irb):1

Am i missing something here…a gem?

I use rails 2.2.

remco