does iTunes DRM depend on the wifi connection with which the purchase was made This might be a fairly specific question but my WiFi card was having issues (the Wifi:No Hardware Installed error). I started using an usb wifi adapter. The issue is that now none of my iTunes media is playable. I suspect that these are tied to the the hardware WITH the specific mac address but this seems unreasonable (ie to have Apple fix it and have my laptop for several days)? Is this the issue? Is there a workaround? Can I reauthenticate it? The error I get is:
Blatantly stolen from Apple's support website, Make sure iTunes is closed and go into your iTunes folder and delete the following files:

iTunes Library Extras.itdb
iTunes Library Genius.itdb

You may even have an additional "Extras" file with a time/date stamp on it and delete that as well.

Of course, please do this at your own risk of losing any preferences that these files may contain. I don't know exactly what these files do, but I've done this fix for a number of iTunes related issues and it works almost every time.

Hope this helps!

Apple Support Community