Apple has announced that they are going to reset iTunes to match iCloud libraries on Monday, 26th of September. The image you see above has just appeared on iTunes as note of the reset. Also to note this reset Apple has sent emails to iTunes Match subscribers.
Apple has said that it is necessary to rest the iTunes Match libraries to improve their service. The rest is scheduled to happen at 9AM PDT/ 10AM PST and Apple says that all users of iTunes Match service will need to turn off the service on both their Macs and iOS devices. The song that are saved on the users’ device but not on the cloud will not be affected. This reset is considered to be the final preparation for an early mid-October launch on the iCloud and iOS 5. Other iCloud details is expected to be announced at the October 4th iPhone 5 event.