Any Idea what that means? :
Quite literally what is says. If the motion sensor is asleep (which it probably is, if battery-powered), it will not listen for commands and thus cannot be polled.
I am also getting this mesage on two of my sensors, “Cannot send command to node”, what do i need to do to wake them up, and why do I only see this when I do a manual ‘Poll Now’ ?
Why does it not tell me automatically as it is set (under settings) to … Poll This Node at most once ever 1080 seconds ?
Most likely the device you are polling is sleeping. Either leave it and it will report back when it wakes up, or you can manually wake it up (check the instructions that came with the device on how to wake it up manually)