My G540 starts up in red 'Fault' mode.

I have to press the e-stop and then release it for it to go into the green 'Power' mode. I need to do this only once.

I initially had a cheap e-stop, but have since got a Schneider fancy one, and it's behaving the same way. So it's definitely not the e-stop that's the problem. Any idea what might be happening?