loading mailman fails when including rails application

[allicon]

Error Output

I, [2013-10-09T10:32:48.726882 #7407]  INFO -- : Mailman v0.7.0 started
I, [2013-10-09T10:32:48.727063 #7407]  INFO -- : Rails root found in /RAILS_ROOT, requiring environment...
I, [2013-10-09T10:32:55.412775 #7407]  INFO -- : POP3 receiver enabled (mail@test.de).
/usr/local/rvm/gems/ruby-1.9.3-p392@gemset/gems/mailman-0.7.0/lib/mailman/application.rb:83:in `run': cannot load such file -- mailman/receiver (LoadError)
    from /usr/local/rvm/gems/ruby-1.9.3-p392@gemset/gems/mailman-0.7.0/lib/mailman/application.rb:11:in `run'
    from mailman_app.rb:23:in `<main>'

Script

require 'mailman'

Mailman.config.rails_root = File.expand_path('../../RAILS_ROOT',  __FILE__)
Mailman.config.poll_interval = 10
Mailman.config.maildir = 'Maildir'

Any Ideas to solving that issue?

Thanks, Sebastian

[Mic92]

What is in your load path? puts $: