I've discovered the same difficulty when using MP3's from a semi-DRM source (bought legally, but "claimed" to have no DRM). You might find that these self-same files won't play on a separate player if transferred to USB.
Regardless, if you load the file into Audacity then choose 'Export File as .MP3', then you'll be able to read/edit the new file with the friendlier WavePad.
Doesn't make a lot of sense, but work-around's seldom do.