Write system variables by Focas2

Hello, I need help.

I'm building a kind of monitoring system for NC Machine(5 axis milleing, Fanuc 31iB).

In this system it monitors loadrate and when the loadrate is bigger than I expect the machine should be stop.

So I'm trying to make alarm or the machine stop by Focas2. (I'm using ethernet communication with Focas2 for this system.)
I would like to use system variables #3000 or #3006 to make alarms or masseges.

But I couldn't.

I used for this the Focas function, cnc_wrmacro, and the description says that it can be used for system variables(#1000~#9999).
Other system variables, #3001, #3002 and etc, works well. I can write some value with cnc_wrmacro function.

But when I try to write some value to #3000 ro #3006 EW-NUMBER(3) error is returned. That means the number of variable is wrong.

If there is anyone who are good at using Focas, please give me a idea.

Thank you in advance.