The first thing to check is your encoding settings in Windows Media Player. Open Tools/Options, and click the Copy Music tab. Then make sure that "Protect Music" is unchecked. This will prevent your continuing creation of DRM-ed files that encounter license issues.
But that won't rescue your old files; they'll have to be re-ripped after you change the settings (you could also re-rip to MP3, if WMA gives you too many proglems). An alternative to re-ripping could be to try Tools/License Management and Restore your licenses for purchased music.
Anything that can't be recovered that way might have been downloaded from a P2P service after having been uploaded by someone who left "Protect Music" turned on. I recommend NEVER ripping to a DRM-ed format; situations such as this are becoming more and more common.
Eliot Van Buskirk
I have a dell dimension desktop 4200, running windows xp, with a cd and dvd drive, I use realone and real rhapsody as well as roxios media creater. I downloaded 1.5 gb of music to my hard drive, from my own cd's that I bought and own. Recently I have been finding that a lot of my music is gone! I get a message saying that my license has expired. Someone told me this was due to DRM since it was downloaded originally to WMA player and I never did "tag" or "ID" my music. I never did understand what that means, and I still don't! HELP!