code: function writeSimpleException(requestId, requestType, exceptionMessage, exceptionType) {
  	return protocol.implodeMessage(requestId, requestType,
  		protocol.encodeMetadataException(exceptionType),
  		protocol.encodeString(exceptionMessage));
  }
docs: Encodes an unsuccessful reply.
  
  @param {String} requestId the originating request id
  @param {String} requestType the originating request method name
  @param {String} exceptionMessage the exception message
  @param {String} [exceptionType] the exception type. Allowed values: access, credits
  @return {String} the encoded message
  @private