Kaminari / ActiveRecord Scope conflict

[volontarian]

I got an exception from the dependency kaminari of active_admin on "rails server":

/home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activerecord-3.1.0/lib/active_record/named_scope.rb:194:in `valid_scope_name?': private method `warn' called for nil:NilClass (NoMethodError)
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activerecord-3.1.0/lib/active_record/named_scope.rb:175:in `scope'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/kaminari-0.12.4/lib/kaminari/models/active_record_extension.rb:15:in `block in inherited'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/kaminari-0.12.4/lib/kaminari/models/active_record_extension.rb:10:in `class_eval'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/kaminari-0.12.4/lib/kaminari/models/active_record_extension.rb:10:in `inherited'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/bundler/gems/Import-b0fb88235fb9/lib/import/no_relation.rb:2:in `'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/bundler/gems/Import-b0fb88235fb9/lib/import/no_relation.rb:1:in `'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `block in require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:223:in `block in load_dependency'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:640:in `new_constants_in'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:223:in `load_dependency'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/bundler/gems/Import-b0fb88235fb9/lib/import.rb:5:in `'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:68:in `require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:68:in `block (2 levels) in require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:66:in `each'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:66:in `block in require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:55:in `each'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler/runtime.rb:55:in `require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/bundler-1.0.20/lib/bundler.rb:123:in `require'
    from /home/murdoch/workspace/rails/affily.at/config/application.rb:7:in `'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/railties-3.1.0/lib/rails/commands.rb:52:in `require'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/railties-3.1.0/lib/rails/commands.rb:52:in `block in '
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/railties-3.1.0/lib/rails/commands.rb:49:in `tap'
    from /home/murdoch/.rvm/gems/ruby-1.9.2-p290@affily.at/gems/railties-3.1.0/lib/rails/commands.rb:49:in `'
    from script/rails:6:in `require'
    from script/rails:6:in `'