def _FormatDateTime(self, event):
    """Formats the date to a datetime object without timezone information.

    Note: timezone information must be removed due to lack of support
    by xlsxwriter and Excel.

    Args:
      event (EventObject): event.

    Returns:
      datetime.datetime|str: date and time value or a string containing
          "ERROR" on OverflowError.
    """
    try:
      datetime_object = datetime.datetime(
          1970, 1, 1, 0, 0, 0, 0, tzinfo=pytz.UTC)
      datetime_object += datetime.timedelta(microseconds=event.timestamp)
      datetime_object.astimezone(self._output_mediator.timezone)

      return datetime_object.replace(tzinfo=None)

    except (OverflowError, ValueError) as exception:
      self._ReportEventError(event, (
          'unable to copy timestamp: {0!s} to a human readable date and time '
          'with error: {1!s}. Defaulting to: "ERROR"').format(
              event.timestamp, exception))
      return 'ERROR'