I had the same issue. My BnG saw my NAIS as another boat. If you change the MMSI in the transponder reciver you need to go to the BnG Zeus menu, I think it's under a settings submenu, and put your MMSI in there.
You can not (in the USA) put a MMSI in a transponder reciver without a FCC licsense. So I thought initially I was screwed. You can, I found out enter your own MMSI into your BnG.
Please be aware you may have the same issue with the radio
This all started with my BnG VHF
going bad doing an upgrade, they sent me a new one, upgradded and blank, and I 'smartly'
decided to change the MMSI from the previous owner to my MMSI. This resulted in collision
alarms because the radio
has an AIS reciever as well. I had 3 BnG 'experts' out to the boat and they changed the MMSI on the NAIS for me but put a 0 instead of an 8 in it.
Many trials and errors later I had the same MMSI in the radio and the NAIS, but then the BnG kept seeing my new Radio/NAIS as a separate boat and I got collision
alarms on the radar
I finally went thru the BnG menus at the helm
and go to a place where it let me enter my MMSI. I did so and problem was solved
If I get to the boat this week ill try to find that sub menu and post pics/step by step.
Please look very closely at the MMSI the 0 and 8 admittedly look very similar. Also do you have a hand held on the boat that could send out AIS or other device?