Redmine 500 error (undefined method `issue_category_tree')

[Gumis91]

Hello,
I'm having difficult time trying to use your plugin. As long as project have no categories, it's settings page is working fine. However, when I'm trying to add new category or open project with already exiting categories, Redmine 500 error occurs.

Message from system log:

Started GET "/projects/test_backend/settings/categories" for 10.132.182.41 at 2016-04-27 16:49:09 +0200
Processing by ProjectsController#settings as HTML
  Parameters: {"id"=>"test_backend", "tab"=>"categories"}
  Current user: kkuziel-admin (id=77)
  Rendered plugins/redmine_meeting_room_calendar/app/views/projects/_project_meeting_rooms.html.erb (0.7ms)
  Rendered projects/_form.html.erb (38.8ms)
  Rendered projects/_edit.html.erb (40.8ms)
  Rendered projects/settings/_modules.html.erb (12.9ms)
  Rendered projects/settings/_members.html.erb (21.5ms)
  Rendered plugins/advanced_roadmap_v2/app/views/projects/settings/_milestones.html.erb (2.5ms)
  Rendered projects/settings/_versions.html.erb (13.9ms)
  Rendered plugins/redmine_category_tree/app/views/projects/settings/_issue_categories.html.erb (564.8ms)
  Rendered common/_tabs.html.erb (665.0ms)
  Rendered projects/settings.html.erb within layouts/base (666.5ms)
Completed 500 Internal Server Error in 687ms (ActiveRecord: 14.7ms)

ActionView::Template::Error (undefined method 'issue_category_tree' for #<#<Class:0x000000052568e0>:0x007f5b39ed1458>):
    10:     <th></th>
    11:   </tr></thead>
    12:   <tbody>
    13: <% issue_category_tree(@project.issue_categories) do |category, level| %>
    14:   <% unless category.new_record? %>
    15:   <tr class="issue_category <%= cycle 'odd', 'even' %> <%= level > 0 ? "idnt idnt-#{level}" : nil %>">
    16:     <td class="name"><span><%=h(category.name) %></span></td>
  app/views/common/_tabs.html.erb:22:in 'block in _437c7bed7810a622c4d4f1b69fd38128'
  app/views/common/_tabs.html.erb:21:in 'each'
  app/views/common/_tabs.html.erb:21:in '_437c7bed7810a622c4d4f1b69fd38128'
  app/helpers/application_helper.rb:321:in 'render_tabs'
  app/views/projects/settings.html.erb:3:in '_1c3d66c0fad385775d8e22882599a759'

Details of my installation:

  Redmine version                3.0.7.stable
  Ruby version                   2.2.4-p230 (2015-12-16) [x86_64-linux]
  Rails version                  4.2.3
  Environment                    production
  Database adapter               PostgreSQL
SCM:
  Git                            1.8.3.1
  Filesystem                     
Redmine plugins:
  a_common_libs                  2.0.0
  advanced_roadmap_v2            2.4.1
  copy_parent_issue_id           1.0.1
  event_notifications            3.0.0
  favorite_locations             0.0.1
  inline_edit_issues             0.0.1
  issue_votes                    0.2.0
  mega_calendar                  1.3.1
  redmine_agile                  1.3.12
  redmine_banner_notifications   0.0.1
  redmine_base_deface            0.0.1
  redmine_base_select2           4.0.0
  redmine_better_crossprojects   0.4
  redmine_category_tree          0.0.6
  redmine_checklists             3.1.3
  redmine_contacts               4.0.4
  redmine_custom_reports         3.1.0
  redmine_custom_values_projects 0.0.1
  redmine_custom_workflows       0.1.6
  redmine_dashboard              2.7.0
  redmine_default_custom_query   1.1.2
  redmine_default_subtask_tracker 0.2
  redmine_image_clipboard_paste  1.0.0
  redmine_improved_searchbox     0.0.3
  redmine_issue_tabs             1.1.1
  redmine_issue_templates        0.1.1
  redmine_logs                   0.1.0
  redmine_mail_reminder          3.0.0.0001
  redmine_meeting_room_calendar  3.0.0
  redmine_merge_redmine          0.0.1
  redmine_monitoring_controlling 0.1.1
  redmine_my_page                0.1.8
  redmine_pivot_table            0.0.2
  redmine_pretend                2.0.1
  redmine_questions              0.0.7
  redmine_related_issues         0.0.1
  redmine_scheduling_poll        1.3.0
  redmine_sidebar_toc_pt         1.7.0
  redmine_subtasks_inherited_fields 1.1.0
  redmine_tab                    0.4.0
  redmine_tags                   3.1.0
  redmine_timelog_updates_issue  0.1
  redmine_timesheet_plugin       0.7.0
  redmine_workflow_enhancements  0.5.0
  redmine_xls_export             0.2.1.t9
  redrisk                        1.0.1
  release_logs                   1.0.0
  tracker_hider                  0.0.1
  wiking                         1.1.0

Any ideas what may be causing this issue?
Thanks in advance!

[Shinjaewon]

redmine_category_tree/app/views/projects/settings/_issue_categories.html.erb

1line add code
<% self.class.send(:include, RedmineCategoryTree::IssueCategoryHelper) -%>

[aozhi2nd]

add under line 12