Similar problems have occured before, see:
http://discussions.info.apple.com/message.jspa?messageID=10837099
I had the same problem on both my work computer (XP) and my home computer (Vista). On my work computer, I uninstalled iTunes and installed the latest version, which seems to have fixed the problem. I haven't had time to try this on my home computer, not the tip by njselkie in the linked thread above either.
Somehow, I wonder if this problem is connected to the daylight saving time, or rather the switch to or from daylight saving time. From the linked thread, it seems that many people had the problem at the end of March, and now this happens again at the end of October. From other answers, it seems that if the computer time and timezone settings are wrong, there can be a problem with the iTunes store. Maybe this works the other way as well, i.e. if the computer time is correct but doesn't sync with... well... something connected to iTunes or the iTunes store.