Ahh, think I see what you are saying - I have had a couple like that as it goes.... You try to open em in WMP and either get "cannot play blah blah" or it doesn't do anything and turns red (in the right pane listing)

Here's what I do, which more often than not surprisingly works;

Download SWITCH from here : http://www.nch.com.au/switch/index.html

And convert the files into MP3 (at say, 192k or whatever) and select a new place to save em (create a new folder, or whatever, so long as not in the same location)

If it starts working then let it run. Sometimes of course, the files are completely fucked and you can do nothing. But often, the info part is fucked, but the actual music part is okay (just the packaging is fubar) so they will convert, and then play fine)

Worth a shot anyway