Can't get .midi files to play using PlayMusic

All tests in the DXDiag work OK.

I have an older game that I wrote in C++ that uses DirectX to play .mid files and that game runs fine (music plays).

Also, I tried this:

chnCool=PlayMusic("cool.wav")
If chnCool = 0 Then RuntimeError("wav file not loaded")
chnTitle=PlayMusic("Title.mid")
If chnTitle = 0 Then RuntimeError("mid file not loaded")
WaitKey()
End

And the wav file plays but the mid file doesn't (and I get the 'mid file not loaded' message).
Both files are in the same directory as the exe. It's not making sense.