My memory is that the AP24 connects to, and is powered by, a SimNet bus. Simnet is Simrad's implementation of a NMEA 2000 compatible system. The Simnet connectors, unlike other NMEA 2000 and compatible systems, don't screw in or on. Instead, they just push in -- and pull out.
So, I guess my next questions are...
What autopilot computer do you have?
Did you do anything physical other than make menu choices? Peek behind anything? Pull anything out to llook? Etc?
Since the AP24 is displaying thenerror.message, it is receiving power, which means it is connected to the NMEA 2000 -compatible bus, and that bus, itself, is powered.
If you touched anything physical, I'd look there first for an unplugged or loose cable. The AP24 does let one daisy chain off of the back of it, as do many of the Simrad devices. SO, I'd also check the back just to make sure it isn't directly connected to the AP computer in addition to the bus. It is possible the computer connects to the bus via the AP24. Not probable, just possible.
If also want eyes on the AP computer. It probablynhas LED indicators for power and status. I'd check those and then it's connections.
The 7612 is fully compatible with NMEA 2000, so no setting should break anything. It also only has one NMEA 2000 port, so it can't do any daisy-chaining or interfere with the connection between the AP computer and AP24.
Good luck!