Error when when viewing project's settings page in Redmine

Question

We recently upgraded Redmine from 2.5.2 to 2.6 but we get an error "Redmine 500 error" when we visit a project's settings page. When I look at the error log this is what I see:

  Started GET "/projects/leaders-premier/settings" for xx.xx.xxx.xxx at 2014-12-09 16:21:58 -0500
  Processing by ProjectsController#settings as HTML
  Parameters: {"id"=>"leaders-premier"}
  Current user: ajankowski (id=3)
  Rendered projects/_form.html.erb (27.8ms)
  Rendered projects/_edit.html.erb (29.8ms)
  Rendered projects/settings/_modules.html.erb (4.7ms)
  Rendered projects/settings/_members.html.erb (77.6ms)
  Rendered common/_tabs.html.erb (117.8ms)
  Rendered projects/settings.html.erb within layouts/base (118.6ms)
    
  Completed 500 Internal Server Error in 268.9ms

    ActionView::Template::Error (The single-table inheritance mechanism failed to locate the subclass: 'GroupNonMember'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Principal.inheritance_column to use another column for that information.):
        77:       </p>
        78:       <%= javascript_tag "observeSearchfield('principal_search', null, '#{ escape_javascript autocomplete_project_memberships_path(@project, :format => 'js') }')" %>
        79:       <div id="principals_for_new_member">
        80:         <%= render_principals_for_new_members(@project) %>
        81:       </div>
        82:       <p>
        83:         <%= l(:label_role_plural) %>:
      app/helpers/members_helper.rb:25:in `render_principals_for_new_members'
      app/views/projects/settings/_members.html.erb:80:in `block in _app_views_projects_settings__members_html_erb__3521341374444963390_113866560'
      app/views/projects/settings/_members.html.erb:69:in `_app_views_projects_settings__members_html_erb__3521341374444963390_113866560'
      app/views/common/_tabs.html.erb:22:in `block in _app_views_common__tabs_html_erb___1280924502012219319_110275440'

We even went back to 2.5.2 and we still get the same error. Anyone have any idea what is causing the issue?

Answer 1

When I upgraded and then downgraded it must have created two new groups. I deleted the following groups from the users table: GroupNonMember and GroupAnonymous and the problem went away.