Indeed, those sound commands seem to be extremely temperamental.
I couldn't get my custom sounds in Village Depacification to work at first. Whereas most editors defined the text to be displayed with sounds in description.ext, I though I would save time by leaving those portions blank and used the scripted sideChat commands that I had written much earlier. Some (but bizarrely, not all) sounds would not work until I cut out the sideChat and defined the text in description.ext in the normal way.
If you can't get sound to work, I recommend a line-by-line comparison with any mission with working custom sounds.