Steps to reproduce:
1. Open the attached project (Asteroids.zip)
2. Try to import audio files (from Assets/mySounds/)
3. Observe an error message in the Console window:
Unspecified error during import of AudioClip Assets/mySounds/Explosion+5.wav

Note:
Audio files have Modified date in the past (1901-12-13), it causes the issue

Workaround:
The 'touch' on Linux or 'COPY /B filename.ext +,, filename.ext' on Windows will fix the issue

Expected result: Audio file should be imported
Actual result: Console window gives an error message

Reproduced with: 5.3.7p3, 5.4.3p4, 5.5.0f3, 5.5.0p3, 5.6.0b3

Fixed in: 2017.3.0p2