s10u10 ntp server warning on /var/adm/messages - "receive: aspiring active peer not authenticated"

Question:Why the WARNING message "xntpd[xxxx]: [ID xxxxxx daemon.warning] receive: aspiring active peer not authenticated" on "/var/adm/messages" ntpserver files.

 This is my NTP servers infrastructure (xx.xx.xx.0/24 is the net of my ntp server):

      +----------------------------+
     | timevault GPS source clock |
     |         (Stratum 1)        |
     +--------------+-------------+
                    |.101
                    |               +---------------------+
                    |               | pd1ntpsrv01 SF V240 |
           defgw .3 +---------------+     (Stratum 2)     |
                    |           .102+---------------------+
                    |                           
                    |.103
         +----------+----------+
         | pd1ntpsrv02 SF V240 |
         |     (Stratum 2)     |
         +---------------------+               

root@pd1ntpsrv01 # egrep -v ^# /etc/inet/ntp.conf && cat /etc/release && uname -a
server timevault minpoll 4 maxpoll 6 prefer
peer pd1ntpsrv02 minpoll 4 maxpoll 6 key 20
driftfile /var/ntp/ntp.drift
trustedkey 20 1
keys /etc/inet/ntp.keys