r-labs » Work Time

１日前から使用させていただいています。
インストール直後はに使えていたのですが、あるタイミングから突然
500エラーが発生するようになってしまい、WorkTime経由の工数入力、管理画面のプラグイン設定画面がともにできなくなってしまいました。
具体的には、プロジェクトの「工数」リンククリック時、および管理画面の「プラグイン」メニューでWorkTimePluginの「設定」リンクをクリックした時点で500エラー画面が出てきてしまいます。

ログを抜粋したものを添付します。

----------------------------
Processing by ProjectsController#settings as HTML
Parameters: {"id"=>"*******"}
Current user: * (id=7)
Rendered projects/_form.html.erb (19.6ms)
Rendered projects/_edit.html.erb (21.1ms)
Rendered projects/settings/_modules.html.erb (7.4ms)
Rendered projects/settings/_members.html.erb (32.2ms)
Rendered projects/settings/_versions.html.erb (3.6ms)
Rendered projects/settings/_issue_categories.html.erb (2.0ms)
Rendered projects/settings/_wiki.html.erb (1.6ms)
Rendered projects/settings/_repositories.html.erb (1.8ms)
Rendered projects/settings/_boards.html.erb (1.8ms)
Rendered projects/settings/_activities.html.erb (14.2ms)
Rendered plugins/redmine_work_time/app/views/settings/_work_time_project_settings.html.erb (1.5ms)
Rendered common/_tabs.html.erb (94.9ms)
Rendered projects/settings.html.erb within layouts/base (95.5ms)
Completed 500 Internal Server Error in 116ms (ActiveRecord: 8.5ms)

ActionView::Template::Error (no implicit conversion of Symbol into Integer):
1: <%
2: if Setting.plugin_redmine_work_time[:account_start_days] &&
3: Setting.plugin_redmine_work_time[:account_start_days][@project.id.to_s]
4: day = Setting.plugin_redmine_work_time[:account_start_days][@project.id.to_s]
5: else
plugins/redmine_work_time/app/views/settings/_work_time_project_settings.html.erb:2:in `[]'
plugins/redmine_work_time/app/views/settings/_work_time_project_settings.html.erb:2:in `_plugins_redmine_work_time_app_views_settings__work_time_project_settings_html_erb___3380772684252180802_70127373643860'
app/views/common/_tabs.html.erb:22:in `block in app_views_common_tabs_html_erb___1097984621120188256_70127569988400'
app/views/common/_tabs.html.erb:21:in `each'
app/views/common/_tabs.html.erb:21:in `_app_views_common__tabs_html_erb___1097984621120188256_70127569988400'
app/helpers/application_helper.rb:324:in `render_tabs'
app/views/projects/settings.html.erb:3:in `_app_views_projects_settings_html_erb__811850956576166087_70127570037700'
lib/redmine/sudo_mode.rb:63:in `sudo_mode'

Completed 500 Internal Server Error in 14ms (ActiveRecord: 2.4ms)

TypeError (no implicit conversion of Symbol into Integer):
plugins/redmine_work_time/app/controllers/work_time_controller.rb:447:in `[]'
plugins/redmine_work_time/app/controllers/work_time_controller.rb:447:in `prepare_values'
plugins/redmine_work_time/app/controllers/work_time_controller.rb:37:in `show'
lib/redmine/sudo_mode.rb:63:in `sudo_mode'