Redmine

I upgraded my Redmine from 2.4 to 3.3.1 (Windows) recently which worked without problems. Migrated database and plugins and all seems fine. However I cannot delete wiki pages anymore. Clicking the "delete" link gives me an Error 500. The production log says:

Started DELETE "/projects/project-name/wiki/This_is_a_page" for 127.0.0.1 at 2017-01-09 10:00:07 +0100
Processing by WikiController#destroy as HTML
  Parameters: {"authenticity_token"=>"21PlecTGZHu4zJVT04z9AmtOlEKqdXvG0N3dppkdFYWfdJWx+5UTG9qoMJbtU25QsfUgakTt+b9tVyzfKpfY+Q==", "project_id"=>"project-name", "id"=>"This_is_a_page"}
  Current user: itsme (id=1)
Completed 500 Internal Server Error in 47ms (ActiveRecord: 31.2ms)

ActiveRecord::RecordNotDestroyed (Failed to destroy the record):
  app/controllers/wiki_controller.rb:278:in `destroy'
  lib/redmine/sudo_mode.rb:63:in `sudo_mode'

Any ideas why / how I can solve this? I'm admin on that installation.
My setup is running on a Windows Server. Using Thin as webserver.

Environment:
  Redmine version                3.3.1.stable
  Ruby version                   2.1.9-p490 (2016-03-30) [i386-mingw32]
  Rails version                  4.2.7.1
  Environment                    production
  Database adapter               Mysql2
SCM:
  Filesystem                     
Redmine plugins:
  localizable                    0.4.0
  redmine_checklists             3.1.5
  redmine_issue_templates        0.1.3
  redmine_ldap_sync              2.0.8.devel
  redmine_silencer               0.4.1
  redmine_startpage              0.1.0
  redmine_wiki_extensions        0.7.0
  redmine_wiki_html_util         0.0.1
  selux_extensions               0.1.0