internal server error 500 due to invalid date

[stefankuhr]

Hello, we use the better gantt chart plugin version 0.90 with redmine 2.5.1.stable, ruby version 1.9.3-p194 (2012-04-20) [i486-linux] and rails version 3.2.6 on a debian wheezy system. For one user, we always get an internal server error if she clicks the gantt tab in her project. The log file entry is as follows:

Started GET "/redmine/projects/sysew/issues/gantt" for 10.22.128.145 at 2015-07-20 15:48:36 +0200
Processing by GanttsController#show as HTML
Parameters: {"project_id"=>"sysew"}
Current user: schreier (id=87)
Rendered queries/_filters.html.erb (21.9ms)
Rendered plugins/redmine_better_gantt_chart/app/views/gantts/show.html.erb within layouts/base (606.2ms)
Completed 500 Internal Server Error in 805.3ms

ActionView::Template::Error (invalid date):
154: work_days = @gantt.work_days_in(Date.new(year + 1), @gantt.date_from)
155: months_remaining -= 12 - (@gantt.date_from.month).to_i - 1
156: elsif months_remaining < 12
157: work_days = @gantt.work_days_in(Date.new(year, months_remaining+1, 1), Date.new(year))
158: months_remaining = 0
159: else
160: work_days = @gantt.work_days_in(Date.new(year + 1), Date.new(year))
plugins/redmine_better_gantt_chart/app/views/gantts/show.html.erb:157:in new' plugins/redmine_better_gantt_chart/app/views/gantts/show.html.erb:157:inblock in _plugins_redmine_better_gantt_chart_app_vi$
plugins/redmine_better_gantt_chart/app/views/gantts/show.html.erb:150:in times' plugins/redmine_better_gantt_chart/app/views/gantts/show.html.erb:150:in_plugins_redmine_better_gantt_chart_app_views_gantt$
/usr/lib/ruby/vendor_ruby/action_view/template.rb:145:in block in render' /usr/lib/ruby/vendor_ruby/active_support/notifications.rb:125:ininstrument'
/usr/lib/ruby/vendor_ruby/action_view/template.rb:143:in `render'

Can someone please shed some light on this and tell me what is going wrong? I am not at all an expert in ruby/rails, so I don't have the faintest idea what's going wrong.

Best regards,

Stefan Kuhr