Having iTunes authorization problems? Files downloaded from the iTunes Store can only be authorized to play on 5 computers at a time. If you try to go over 5 computers, then iTunes will give you an authorization error like this [pic].
For most people, 5 computers is plenty. Where you really start to run into authorization problems is when you get a new computer or your current computer dies. Before you sell, donate or get rid of an old computer, you should always “deauthorize” it first in iTunes. You should even consider deauthorizing your computer before sending it away for repair or upgrade – in case it doesn’t come back in one piece. Deauthorizing your computer does not erase your music files; it simply prevents your purchased music from playing until you authorize that computer again with your iTunes password.
This tutorial will walk you through the entire iTunes Deauthorizing process.