Can't play MP3s?

[saturnine64]

I've just purchased the Limewire Pro for the special offer of $14.95. Maybe this was a mistake? The problem is that Limewire works perfectly(excellent connection; no firewall detected), but I can't play any of the MP3s that I've downloaded with Quicktime, Windows Media player or iTunes. I never had this problem with the old Limeware software, so what's the problem? Further, when I attempt to play the downloaded files, a msg pops up saying: "The file you are attempting to play has an extension that does not match the file format. Playing the file may result in unexpected behaviour." This msg isn't coming from Limewire. Alternatively, a software program entitled mp3z.com or Mirar pops up and asks me to download. Is this malicious adware? My Norton blocks it and reports it as WhenU. Can anyone help?