404 when accessing configuration page

[david-pettifor-nd]

Installed the plugin (rake command picked it up) and I can see it listed in the plugins list. When I click on "Configure" I get a 404 error. Here's what the log file shows:

Started GET "/redmine/settings/plugin/redmine_omniauth_cas" for xx.xx.xx.xx at 2018-11-26 11:13:04 -0500
Processing by SettingsController#plugin as HTML
  Parameters: {"id"=>"redmine_omniauth_cas"}
  Current user: xxxxxxxx (id=8)
  Rendered settings/plugin.html.erb within layouts/admin (3.0ms)
Missing template, responding with 404
  Rendered common/error.html.erb within layouts/base (0.6ms)
Completed 404 Not Found in 54ms (Views: 11.9ms | ActiveRecord: 14.4ms)

When I do a find for the missing template, I do find it in: ./app/views/settings/plugin.html.erb (relative to the redmine root dir)

Version info:

Environment:
  Redmine version                3.2.1.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.6
  Environment                    production
  Database adapter               PostgreSQL
SCM:
  Git                            2.7.4
  Filesystem                     
Redmine plugins:
  redmine_omniauth_cas           3.3.0