twitter outbound

how can we send message to twitter account from our application.I am
using twitter4r gem there is one message method in which we can post
but it's showing me following error

  @twitter.message(:post, 'Are you coming over at 6pm for the BBQ
tonight?', '@christy24')

/usr/local/lib/ruby/gems/1.8/gems/twitter4r-0.3.0/lib/twitter/client/
base.rb:34:in `raise_rest_error': Forbidden (Twitter::RESTError)
        from /usr/local/lib/ruby/gems/1.8/gems/twitter4r-0.3.0/lib/
twitter/client/base.rb:39:in `handle_rest_response'
        from /usr/local/lib/ruby/gems/1.8/gems/twitter4r-0.3.0/lib/
twitter/client/base.rb:13:in `http_connect'
        from /usr/local/lib/ruby/1.8/net/http.rb:547:in `start'
        from /usr/local/lib/ruby/gems/1.8/gems/twitter4r-0.3.0/lib/
twitter/client/base.rb:9:in `http_connect'
        from /usr/local/lib/ruby/gems/1.8/gems/twitter4r-0.3.0/lib/
twitter/client/messaging.rb:73:in `message'
        from (irb):6:in `irb_binding'
        from /usr/local/lib/ruby/1.8/irb/workspace.rb:52:in
`irb_binding'
        from /usr/local/lib/ruby/1.8/irb/workspace.rb:52