FIX FOR ERROR (-208) - DEFINITIVE ANSWER!!
After having checked my other computer for what files had been altered or created this last day (during thich i had successfully authorized it for playback in preview and for purchased music) i found the file "SC Info.sidb" under "X:\Documents and Settings\All Users\Application Data\Apple Computer\iTunes\SC Info". This appears to hold your authorization keys or some other magic stuff. By deleting this files parent folder, iTunes was forced into asking me to authorize this computer again for playback, with the difference this time that there were some other options on the authorization dialog, just like there should be when for the first time authorizing a computer to play protected iTunes content. When I then entered my information as always and was expecting to see the same -208 error, i was instead greeted with sweet opera that I had been longing to listen to.
A minute or so later, I found this article on the net:
http://nslog.com/archives/2003/05/02/authorizingitunes_scinfo.php
It describes the same problem, but for users of macs, but the same principle applies to windows machines. The only thing fifferent is the paths to the key database. "I:\Documents and Settings\All Users\Application Data\Apple Computer\iTunes\SC Info"
Try the same procedure and hopefully your iTunes copy should work again. Just remember to make sure all iTunes related processes are shut down first before trying this. It might not matter, but that is what I did.