How to correctly use "Display message" task on ERA?

[Vorbarra 0]

Hello

I want to know how to correctly use the "Display message" task on ERA, because I want to warn my clients when I'm going to execute a task, for example:

To make an on demand scan I want to display a message warning my client about the scan and don't turn off the computer.

I tried making a task but it fails to execute it says this: 

This is a test on 2 computers

What am I doing wrong?

[mahiralkhoir 4]

I think display message task in ERA depend on "net send" windows