I/O error 32 on importing some MP3s

I am trying to build a console Doom music WAD for myself with the MP3 files of PSX Doom and Doom64 music but on some of the former's files while replacing (raw data), I get the error above on various files. The one I try to import is about 9 minutes long but the Staging Area MP3 (which is 16 minutes) imported fine.

What gives?

The files might have been locked by another application - were you auditioning tracks in your music player while importing them?

I did open them individually in WMP but closed it before I imported each track.

Apaprently things are working now, must have been what you described, GreyGhost.