Redmine

Hello,
today our Redmin installation started acting up on us throwing "500 Internal Server Error" when accessing any issue. In the logs we have

Processing IssuesController#show (for 66.xx.x.70 at 2012-06-01 16:54:59) [GET]
  Parameters: {"action"=>"show", "id"=>"10", "controller"=>"issues"}

ActiveRecord::MissingAttributeError (missing attribute: hours):
  app/models/time_entry.rb:54:in `after_initialize'
  app/controllers/issues_controller.rb:125:in `new'
  app/controllers/issues_controller.rb:125:in `show'
  /home/webapp/redmine/public/dispatch.fcgi:24

Rendering /home/webapp/redmine-1.3.0/public/500.html (500 Internal Server Error)

Any idea why it might be and how to eventually solve it?