A standard pcm wav file should work. I had the same problem(Vista64). It seems it's how windows takes it to the sound input(known at smith micro).
This helped at me: I pluged in an external thing like a headphone to the soundcard's line-in and looked in the audio settings to see the record channel is active with the line in connected device. For me it worked too with only a plug and cable without any device at the end of it - very strange. I can't describe the special technical reason here - but it works.