Error on Issue view on RM 2.5.1

[darioo]

I have installed this plugin on RM 2.5.1 and when I go to issue page or I set votes on issues list I always get abn error:

  Rendered issues/show.html.erb within layouts/base (268.1ms)
Completed 500 Internal Server Error in 1395.7ms

ActionView::Template::Error (undefined method `votes_value' for #<Issue:0x00000002e71b00>):
    5:          <% end %>
    6:
    7:    <% if authorize_for('issues', 'view_votes') %>
    8:     <% vv = @issue.votes_value %>
    9:     <%= content_tag('span', vv, :class => (vv > 0? 'votes-positive': ( vv < 0 ? 'votes-negative' : ''))) %>
    10:           <% end %>
    11:
  lib/redmine/hook.rb:111:in `block in render_on'
  lib/redmine/hook.rb:61:in `block (2 levels) in call_hook'
  lib/redmine/hook.rb:61:in `each'
  lib/redmine/hook.rb:61:in `block in call_hook'
  lib/redmine/hook.rb:58:in `tap'
  lib/redmine/hook.rb:58:in `call_hook'
  lib/redmine/hook.rb:158:in `call_hook'
  app/views/issues/show.html.erb:55:in `_de0f59f6eb2bba627be68ea1568fcbf3'
  app/controllers/issues_controller.rb:128:in `block (2 levels) in show'
  app/controllers/issues_controller.rb:125:in `show'