Got 1304 error when add subscriber

[fones]

CitrusMail::CitrusMailError: 1304 - Unknown error
    from /usr/lib/ruby/gems/1.9.1/gems/citrus-mail-0.2.1/lib/citrus_mail/response.rb:23:in `process_http_response'
    from /usr/lib/ruby/gems/1.9.1/gems/citrus-mail-0.2.1/lib/citrus_mail/response.rb:8:in `build_from_http_response'
    from /usr/lib/ruby/gems/1.9.1/gems/citrus-mail-0.2.1/lib/citrus_mail/client.rb:51:in `http_post'
    from /usr/lib/ruby/gems/1.9.1/gems/citrus-mail-0.2.1/lib/citrus_mail/list.rb:78:in `make_post_request'
    from /usr/lib/ruby/gems/1.9.1/gems/citrus-mail-0.2.1/lib/citrus_mail/list.rb:23:in `add_subscriber'
    from /home/fones/www/XXX/gateway/app/controllers/users_controller.rb:44:in `subscribe_to_newsletter'
    from (irb):2
    from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.19/lib/rails/commands/console.rb:47:in `start'
    from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.19/lib/rails/commands/console.rb:8:in `start'
    from /usr/lib/ruby/gems/1.9.1/gems/railties-3.2.19/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'