ITunes says my computer and iPod aren't similarly authorized

Question

I'm trying to sync my iPod Touch 2G with iTunes on my Windows XP computer, and I keep getting this message:
"This computer is no longer authorized for apps that are installed on the iPod "Catherine the Great". Would you like to authorize this computer for items purchased from the iTunes Store?
If you do not authorize this computer, 4 apps, including "AIM", and their data will be deleted form this iPod."
There are cancel, authorize, and don't authorize buttons. I can hit cancel but I need to sync my iPod and that's counterproductive, I can hit authorize and be taken to the "Enter Account Name and Password" login bit... I enter my apple ID and password and it says "This computer is already authorized". I even double-checked that it was the same username and password in my iPod and it is, it's what I use to download apps from the iTunes store.
If I hit "don't authorize", it starts the sync but then says it's deleting apps because they're not authorized.
How do I fix this? I've never had this problem before. I haven't synced my iPod in the past two weeks at least, probably a few weeks longer than that, and I have iTunes 10.1.1.4. I don't remember exactly when the last time I upgraded to the latest version of iTunes was, but there's definitely a good chance I haven't tried to sync my iPod since the last time I updated iTunes.

Answer 1

I tried everything it said, but nothing worked. But thank you for the link, I was looking for something along those lines in the Apple Support area and missed it somehow.
I just realized though that when it prompts me to authorize it's my AIM screenname it has in the Apple ID space, even though I don't use that as my Apple ID and, as far as I know, did not ever download anything from the iTunes store with that.
Do you know any way to check if I downloaded any of my apps using a different ID even though I really don't think I did?
I would just deauthorize it and then redownload them all, but some of them aren't available any more and I have data, ebooks, etc. on them.