charts error

Processing ChartsBurndownController#index (for 10.6.104.43 at 2010-07-13 04:06:13) [GET]
  Parameters: {"project_id"=>"pbr", "action"=>"index", "controller"=>"charts_burndown"}

NoMethodError (undefined method `parent_id' for #<Issue:0x7f9d3efedcc8>):
  vendor/plugins/redmine_charts/app/controllers/charts_burndown_controller.rb:79:in `get_data_for_burndown_chart'
  vendor/plugins/redmine_charts/app/controllers/charts_burndown_controller.rb:74:in `each'
  vendor/plugins/redmine_charts/app/controllers/charts_burndown_controller.rb:74:in `get_data_for_burndown_chart'
  vendor/plugins/redmine_charts/app/controllers/charts_burndown_controller.rb:8:in `get_data'
  vendor/plugins/redmine_charts/app/controllers/charts_controller.rb:107:in `create_chart'
  vendor/plugins/redmine_charts/app/controllers/charts_controller.rb:79:in `index'
  /usr/lib/ruby/1.8/mongrel/rails.rb:76:in `process'
  /usr/lib/ruby/1.8/mongrel/rails.rb:74:in `synchronize'
  /usr/lib/ruby/1.8/mongrel/rails.rb:74:in `process'
  /usr/lib/ruby/1.8/mongrel.rb:159:in `process_client'
  /usr/lib/ruby/1.8/mongrel.rb:158:in `each'
  /usr/lib/ruby/1.8/mongrel.rb:158:in `process_client'
  /usr/lib/ruby/1.8/mongrel.rb:285:in `run'
  /usr/lib/ruby/1.8/mongrel.rb:285:in `initialize'
  /usr/lib/ruby/1.8/mongrel.rb:285:in `new'
  /usr/lib/ruby/1.8/mongrel.rb:285:in `run'
  /usr/lib/ruby/1.8/mongrel.rb:268:in `initialize'
  /usr/lib/ruby/1.8/mongrel.rb:268:in `new'
  /usr/lib/ruby/1.8/mongrel.rb:268:in `run'
  /usr/lib/ruby/1.8/mongrel/configurator.rb:282:in `run'
  /usr/lib/ruby/1.8/mongrel/configurator.rb:281:in `each'
  /usr/lib/ruby/1.8/mongrel/configurator.rb:281:in `run'
  /usr/lib/ruby/1.8/mongrel/command.rb:212:in `run'

Rendering /opt/redmine/redmine-0.9.5/public/500.html (500 Internal Server Error)