for whatever reason it doesn't work for you, you have a temporary/permanent workaround
.
FlashFXP sound event support undocumented feature, instead of selecting .wav files for sounds you can select .bat files. and it's only .bat, not .exe
you can download any program that can generate pc speaker tones and support command line. then you can make .bat file for each sound event, maybe with different tones, and use them instead of .wav or a single beep that flashfxp support.
