rake problemmm?

Hello RoR Developers,

I have problem with rake, I got gettext.rake("lib/tasks") something like

desc 'Create mo files'   task :createmo do     require 'gettext/utils'     require 'gettext/rails'

    GetText.create_mofiles(true, 'po', 'locale')   end end

when I try to use it,gives me error like, rake createmo

(in C:/..../rails) rake aborted! Don't know how to build task 'createmo'

(See full trace by running task with --trace)

what can I do now? what is the problem here..