If you encounter issues with WinAMP not reporting the length of the song in the playlist, it is very likely that the mp3 is corrupt. However, in some cases, this could be due to a bug in WinAMP (I'm using v5.34) disliking unicode characters in the ID3 tags. In my case, an mp3 with the artist's name tagged as Dvořák - diacritics and all and especially the caronned (sic) r - was not gettings its song length displayed next to its title.
Removing the diacritic would have "fixed" the problem. But, I actually left it as it was.