NativeApplication.nativeApplication.systemIdleMode

When I use:

NativeApplication.nativeApplication.systemIdleMode = SystemIdleMode.KEEP_AWAKE;

I get:

Scene 1, Layer 'Layer 1', Frame 1, Line 1 1120: Access of undefined property NativeApplication.

Scene 1, Layer 'Layer 1', Frame 1, Line 1 1120: Access of undefined property SystemIdleMode.

Where is the problem?

Thank you!