Highrez

Full screen application {ALT} {F4} in version 2.17 is invalid. Full screen application {ALT} {F4} must exit before it can take effect.

Sorry, its not clear what you mean.
Are you talking about simulated keystrokes, or the "close window (alt+f4)" option?
If you are NOT using simulated keystrokes, can you try using that, along with {ALT}{f4} and see if that works?

If you are already doing that then I'm afraid I need more information - How about reading the forum rules and filling out the NEW post template so I have some idea of what you are on about?

When the application runs in full screen, such as watching a movie in full screen, the shutdown (ALT + F4) is invalid and must exit the full screen to take effect.

So, your not using simuated keystrokes for this? I'm guessing as you didn't answer me.

When you are full screen does ALT+F4 on the keyboard work as expected or do you still have to exit full screen first?
You could try simulated keystrokes and add {ESC} or whatever key quite full screen before {ALT}{F4}
???