I tried Tetris_all.wav, and yes it has an internal error. This is confirmed because Windows Media Player says the file is corrupt. If Media Player cannot play a wav file, then you know MESS cannot use it either.
Then I tried the IGDemo.wav. The first part loaded fine, however the second part is in a specialised format and didn't load at all.
So, this proves that the driver supports standard cassette files. However for actual driver defects you could talk to the original author who I think is Kale. Remember, the systems are all marked as NOT WORKING.