A while back iTunes required that my account be updated. Up until that time I was using an AIM (AOL Instant Messenger) login ID. Apple required that this account be converted to an Apple account. Went through all this and everything worked fine until the iTunes update back in September (2009). At the same time I was unable to login with my new Apple ID and my music was essentially deauthorized. After a few days the problem that prevented me from logging in was fixed and I was subsequently able to login with my Apple ID.
Here is the problem, much of my music is no longer accessible as it was purchased with the AIM account ID. Almost every time I try to play a track purchased with the AIM ID, a pop up box appears. There is at least one track associated with the AIM ID that currently plays.
Searching for the fix to this situation is frustrating and time consuming. This is a big problem.