JD 3320 Won't Start err 57

[Bohleized]

I have an eHydro that I'm working on, it will run for 2-3 minutes and then shut off with err 57. I checked and cleaned all main electrical connections and tested battery voltage during a key on position. Drops from 12.8 to 12.6 should be fine. I think the only thing left is to change out the controller.

??? Out of ideas ??? HELP

Thanks
Bill