Custom Setting: "Continue Task After Error" does not work

I have imported a tasker project from my mobile phone to an Nvidia shield TV, when I execute the task I get an error message by a "Custom Setting" action:

A1: Custom Setting [ Type:System Name:screen_brightness_mode Value: Use Root:Off Read Setting To:%autobright Continue Task After Error:On ]

results in error:

21.29.47/E Custom Setting: missing 'modify system settings' permission, start proxy
21.29.47/E start proxy ProxyTransparent, wait, time limit 20s
21.29.47/E add wait type Proxy Group time 20
21.29.47/E add wait type Proxy Group done
21.29.47/E set proxy: true (startProxy)
21.29.47/E add wait task
21.29.48/E Error: 1

What I'm wondering is why the task aborts here, even though the checkbox "Continue Task After Error" is set.