Problems with Pixhawk1 and V4.3.7

Wow, the last time I was here must be like years. I have several (5 or so) Pixhawks from back then and I am trying to get one of them set up on a small EAchine racer. I’m using the latest Mission Planner and I think I see an error that refers to the I Meg limit.

I can’t do an ESC calibration. When I press the switch I don’t get the red light and it doesn’t go into calib mode. Given that, I can’t Arm the unit…

What would be the latest firmware that is compatible to the Pixhawk1