use parseJSON instead of parseJson

    success: function (response, status) {
      // Sanity check for browser support (object expected).
      // When using iFrame uploads, responses must be returned as a string.
      if (typeof response == 'string') {
        response = $.parseJson(response);
      }
      return ajax.success(response, status);
    },

This code does not work, it returns a $.parseJson is not a function
The function from jquery is called parseJSON, see http://api.jquery.com/jQuery.parseJSON/