I've found that by following the directory listed in these errors, you can usually either directly find the file it's looking for and correct its name so the game can properly identify it, usually while the game is still running and then hit Retry button,
or, if the file it's looking for either isn't there or you can't tell which one is mis-named, just grab something of a similar size and create a copy then give it the name it's looking for to let it move on.
From what I can tell, it looks like they may be hand-naming and coding and occasionally forget a capital or lowercase. I can remember fixing a few pictures this way in previous versions, I don't think I've ever seen an audio file have this problem though. Neat.