Hi, The title is not totally true. I'm getting trouble to intercept close message on external GUI before execution. I mean, I can detect it with _WinAPI_RegisterWindowMessage and $HSHELL_WINDOWDESTROYED (snippet below) but the Message is already gone and proceed. Because of that, I can't get the ClassName of the external GUI closed. I would like to check the ClassName before executing my code to be sure my function is proceeded on the right GUI. The GUIs i'm watching are all from the same