Validation messages and $.parseJSON(xhr.responseText).errors

Hello!

I try to catch a validation message with a $.parseJSON(xhr.responseText).errors but an alert message hows me “undefined” and I do not understand why.

hier are my validations:

validates :upload_file_name, :presence => true,
:format =>{:with => %r{.(jpg)$}i,:message =>“It should be a pdf File”}

  validates_uniqueness_of :upload_file_name, :message => "blabla"

  validates :upload_file_size,  :inclusion  => {:in =>1.megabytes..20.megabytes,:message=>"bla"}

json:

format.json{ render json: {error: @upload.errors.full_messages}, :status =>422}

and javascript for that:

$(’#fileupload’).fileupload({

        error: function(xhr){
          var errors = $.parseJSON(xhr.responseText).errors
          alert(errors)        
        }
              });

Thanks in advanced