The first thing to check is that the head memory cable is plugged in and in good condition. I usually see a lot of ink building up on those boards and cables over the years and it can short it out.
If that cable looks good, unfortunately you probably have some electrical issues. I would check the head cables for damage or ink splatter and replace if needed. When replacing them I would clean the terminal with alcohol and air duster too. If the head cable looks fine or you replaced it and it still gives that error, it's time to throw parts at it unfortunately. If you know someone who can electronically troubleshoot you might be able to isolate which board is causing the issue but if not, start with the slider board and then the main board. Sometimes this can be because of the head being electronically fried as well. Lets hope it's just a cable!
PS: If you just installed a non Mimaki head and are receiving this error, it's the head.