I have found and fixed an issue with prp_SndClasses: I made PyPRP fall back on Robert's file search method if the internal Blender sound block exists but has somehow become corrupt.
I ran into this problem when I received a blend file from someone who had used the old method of loading sound objects into Blender in the Scene Properties window. He had packed his external data into the blend file but somehow this packing fails for sound objects. His local paths ended up in the sound block but as far as I could tell not the wav files themselves. This gave me the export error: "Cannot locate any sound named <insert long local path here>".
Since I possessed the ogg files in question I expected that dropping them into the same folder as the blend file would solve this problem, but alas... PyPRP stubbornly insisted on using the corrupted sound objects. And unfortunately Blender does not allow the deletion of sound objects (later I realized that renaming them could have worked but by then I had already fixed it in the PyPRP source ).
Christian, do you see a chance to review my fix and still sneak it into the 1.6.0 beta? See rev. 439.