Redmine

I recently submitted an issue about database corruption - #6878

Now I can't seem to properly assign users to groups anymore. I get the following error:

Processing UsersController#edit (for 192.168.0.187 at 2010-12-01 13:59:57) [POST]
  Parameters: {"commit"=>"Save", "action"=>"edit", "authenticity_token"=>"5aVuXTwEiudgRefoIyeBHPXVG9PNB60Yfyx1FIkmDmc=", "id"=>"28", "controller"=>"users", "user"=>{"group_ids"=>["12", ""]}}

ActiveRecord::RecordInvalid (Validation failed: Project can't be blank):
  app/models/group.rb:38:in `user_added'
  app/models/group.rb:33:in `user_added'
  app/models/user.rb:36
  app/controllers/users_controller.rb:101:in `edit'

Is this likely to be a db corruption problem, or is it a new bug in redmine? Any idea how to fix this? I am going to look at the MySQL contents now... maybe there are some broken projects left (thought I deleted them all, maybe they are just invisible).