putting new sounds into the game with sust_sounds. errors

[Herr_today]

Hello.

I used to be able to do this but seem to have forgotten how. I have added sounds into sust using sust_sounds, updating both the .rus and .hdr files. I then change a unit sound to use it but get an error that it is not recognised in the unit on loading the game.

Is there another file in game that I need to add the sound to?