why does this error happened? "incompatible shared memory segment found"

Hi,

    I start 22 programs on the same computer, and some error come out.

    "incompatible shared memory segment found.\n  All applications using NDDS must use compatible shared memory protocols."

    I use the default setting properties for shmem, and QOS setting like this

    datawriter_qos.writer_data_lifecycle.autodispose_unregistered_instances = TRUE;
    datawriter_qos.durability.kind = DDS_VOLATILE_DURABILITY_QOS;
    datawriter_qos.history.kind = DDS_KEEP_LAST_HISTORY_QOS;
    datawriter_qos.history.depth = 10;
    datawriter_qos.resource_limits.max_samples_per_instance = MAX_SAMPLES_PER_INSTANCE;
    datawriter_qos.destination_order.kind = DDS_BY_RECEPTION_TIMESTAMP_DESTINATIONORDER_QOS;

    datareader_qos.durability.kind = DDS_VOLATILE_DURABILITY_QOS;
    datareader_qos.history.kind = DDS_KEEP_LAST_HISTORY_QOS;
    datareader_qos.history.depth = 10;
    datareader_qos.resource_limits.max_samples_per_instance = MAX_SAMPLES_PER_INSTANCE;
    datareader_qos.destination_order.kind = DDS_BY_RECEPTION_TIMESTAMP_DESTINATIONORDER_QOS;

    What is the most posssible reason?