Power supply works well, but the third light is red…

Hello, all.

I have a simodrive power supply which no. is 6SN1145-1BA01-0BA0, version F. It works well, the driver and motor run good with it.

But the third light on that power supply is red. (from top to down: off, yellow, red).

Could you tell me what the problem is and how to fix it?

Thanks a lot and have a nice day.