I got this error after the unit had been installed for 2 years. I tried many ways to troubleshoot the problem, eventually ending up with nothing connected to the unit except for the black ground, the red power, and the yellow continous power. Still, the message persisted.
I removed the deck and looked at the back. There is a bank of wires coming from the circuit board that had visible corrosion bridging the gap between some of the wires. I scraped this corrosion off, and put everything back together and the system works.
It seems that Kenwood didn't make this marine deck to be around a humid environment. I'm wondering if there is a non-conductive coating (epoxy?) that I could coat this circuit board with to prevent reoccurance. Any ideas?