Unable to add songs to iCloud or update iTunes Match.
For the last 4 days I've been unable to add songs to iCloud or update iTunes Match. No matter what I do I get the "We could not complete your iTunes Store request. An unknown error has occurred." message. I've turned iTunes Match off and back on again, signed in and out of my account, etc.
Any clues?
MacBook Pro with Retina display, OS X Mountain Lion (10.8.3), iTunes 11.0.2