Erreur de conversion dans un POST de la tribune

I, [2014-12-13T20:52:09.959413 #17728]  INFO -- :   Parameters: {"board"=>{"message"=>"ah voilà", "object_type"=>"Free"}}
I, [2014-12-13T20:52:09.965636 #17728]  INFO -- : Completed 500 Internal Server Error in 6ms
F, [2014-12-13T20:52:09.967670 #17728] FATAL -- : 
Encoding::UndefinedConversionError ("\xE2" from ASCII-8BIT to UTF-8):
  app/models/board.rb:83:in `encode'
  app/models/board.rb:83:in `clean'
  app/models/board.rb:41:in `save'
  app/controllers/boards_controller.rb:20:in `create'

I, [2014-12-13T20:53:57.122866 #5881]  INFO -- :   Parameters: {"board"=>{"message"=>"Test", "object_type"=>"Free"}}
I, [2014-12-13T20:53:57.129267 #5881]  INFO -- : Completed 500 Internal Server Error in 6ms
F, [2014-12-13T20:53:57.131294 #5881] FATAL -- : 
Encoding::UndefinedConversionError ("\xE2" from ASCII-8BIT to UTF-8):
  app/models/board.rb:83:in `encode'
  app/models/board.rb:83:in `clean'
  app/models/board.rb:41:in `save'
  app/controllers/boards_controller.rb:20:in `create'

I, [2014-12-13T23:22:36.396258 #20198]  INFO -- :   Parameters: {"board"=>{"message"=>"22:22:04@jb3 22:21:42@jb3 ça c'est o
uam avec charset=utf-8", "object_type"=>"Free"}}
I, [2014-12-13T23:22:36.402654 #20198]  INFO -- : Completed 500 Internal Server Error in 6ms
F, [2014-12-13T23:22:36.404711 #20198] FATAL -- : 
Encoding::UndefinedConversionError ("\xE2" from ASCII-8BIT to UTF-8):
  app/models/board.rb:83:in `encode'
  app/models/board.rb:83:in `clean'
  app/models/board.rb:41:in `save'
  app/controllers/boards_controller.rb:20:in `create'