I ask, since without patch, there is no either CACHE\sndlist.dat file, nor "sounds" folder.
But with patch, there are both, and in fact both need to be present (if you remove any file originally part of patched sounds folder, game would complain in similar manner). Same if you remove sndlist.dat, while those files are present.
The thing is, that unlike our little hacks with cutscenes for Precursors and White Gold, when developers add files in sounds folder, they just make new sndlist.dat that is compatible with those files.
Having neither sndlist.dat, nor sounds folder would work too, and it that case game will only use unpatched sounds, that are all stored in gf_sounds.grp.