'(internal) Send an error for a previously sent message.
@param fail: The failure.
@param requestID: The request ID.'

def _sendError(self, fail, requestID):

    if isinstance(fail, failure.Failure):
        if (isinstance(fail.value, Jellyable) or self.security.isClassAllowed(fail.value.__class__)):
            fail = fail.value
        elif (not isinstance(fail, CopyableFailure)):
            fail = failure2Copyable(fail, self.factory.unsafeTracebacks)
    if isinstance(fail, CopyableFailure):
        fail.unsafeTracebacks = self.factory.unsafeTracebacks
    self.sendCall('error', requestID, self.serialize(fail))
