[launchd-dev] launch_msg("CheckIn") IPC failure: Operation not permitted

Hi everyone, I am trying to check in a daemon, with liblaunch. But I am always getting a IPC failure. For now I just tried the samplecode in sampled.c It's just creating a launch_data_t wiht launch_data_new_string(LAUNCH_KEY_CHECKIN); and tries to get a response (launch_msg(msg))) but that returns a NULL and no response. Could somebody give me a hint how to do that. Thanks Thomas