user-led doesn't turn on! (V.6.42.1)

Hi guys,
I have some script that blinks user-led whenever a new user connects to WLAN. I used this command to turn on the mentioned LED:

system leds set type=on numbers=6

It’s been working for quite some time; but recently, I believe after I’ve upgraded my router to latest version (6.42.1), it doesn’t work any more. It shows below error:

input does not match any value of type

I can change type to any other values and it works fine; only “ON” returns error.
Any suggestion will be appreciated.