Further information: It may be that at least some of the problem lies with Virtual DJ, not WavePad, because when I tried to play the same file on Groove Music media player, I got a message that the file was corrupted and could not be played. So I don't want to waste anyone's time trying to solve a problem that may have been created by another app. However, that does not explain the first error message I got on WavePad. Investigation continues, and suggestions still welcome.