When the Import finishes, there is a report.
It will say "Imported ___ new files" "Failed to import ___ files" " ___ files bad "
Click on the checkbox next to "Show in-depth summary" to get exactly which files failed to import (you may need to maximize the window).
I found that audio files that failed or were found to be bad, actually were:
* Corrupt files that won't play in any play (and never played since the corruption occurred on the hard drive )
* Files with embedded cue sheets where the FILE reference in the cue sheet was not the same filename
* Files with filenames or paths that were too long
* Cue files where the FILE reference in the cue file was not the same (usually pointing to a deleted WAV file)