Stamina 2.5 from rapps can not open specific wav files, but others do play fine

VBox4.3.12+AC97 driver from rapps
In the past, Stamina 2.5 from rapps could not play any audio at all.
In 0.4.15-dev-3127-g183566e the situation did improve and most sound and music is playing fine.

But immediately after the startup the app should actually play music already and it fails with that and even pops up an error box about that it had not been able to open the file. (The filename varies with each startup, because the game tries to vary the music), but it will always generate an error-box of the kind:
0.4.15-dev-3127-g183566e_Menu_Georget_Bizet_Carmen_(Les_Toreadors).png
0.4.15-dev-3127-g183566e_Menu_Georget_Bizet_Carmen_(Les_Toreadors).wav.log