Hi
I hate to jump to cause, however my gut feeling is that you have another device, probably a laptop that is configured with the same IP address and when it is plugged in the network, it causes problems like what you see here.
#cd /var/adm
look for the most recent log file of the form nettl.LOG00, you can't view or more this file, you have to use a command called netfmt, there are different switches to look at summary ets - see man netfmt
#netfmt nettl.LOG00
Look for line which says a messge to the effect node with MAC address something is trying to be my IP address.
If my gut feeling is wrong, get EMS and monitor the device, check syslog for messages and use commands such as netstat, lanscan to faultfind. Post an update and we can advise further.
Kind Regards