I have had certain digital files act up on me; not a problem with MIXXX but with the track itself. Sometimes it won't play on a computer with Windows XP and Media Player, but plays fine everywhere else. Sometimes the meta tags have some weird stuff in them -- and who knows what meta information is there that I can't see?
For me, the cheap and dirty way to fix problems like this is to go into an audio editing program (I use Sound Forge, but I believe Audacity will let you do this and it's free). Open up the suspect track, open up a "new" file. Go to the track, hit select all, and copy and paste to the new file. Put in whatever meta tags you want, and save it.
Of course all of this is assuming you actually have the track in your possession. Sometimes iTunes, Rhapsody, and other such programs will let you save it to your iPhone or other device; you can listen to it but you can't save or copy it until it's "purchased." There are all sorts of workarounds, not the least of which is the trusty ol' tape recorder, but depending on the track and the intended usage of it this might be a copyright violation. I'm not condoning theft -- check with BMI if in doubt.