Trying to update to iOS5.0.1, Newsstand content could not be transferred - not authorised

Question

As the strapline says, I am trying to install 5.0.1 update to my iPad, but when i try to sync purchases before doing so (as it will remind me to do if i don't), I get a message saying:
"xxxxx" could not be transferred from the iPad "my iPad" because you are not authorized for it on this computer.
This message occurs for EACH Newsstand subscription I have in my Newsstand folder.
Please don't suggest I deauthorize and reauthorize etc., as the computer i am using IS authorized as I have proven by (a) attempting to reauthorize it , and (b) all my purchased iTunes content works fine.
Any ideas?
What i do NOT want to have to do is redownload gigs of Newsstand content after losing it when i update...

Answer 1

You have items on the iPad that were downloaded or synced to the device that are not in your iTunes library as the message states. That consists of apps, books, videos, songs ....anything that you have downloaded but not yet transferred into iTunes on your computer.
Prior to the latest updates in iTunes, those items would transfer automatically - the overwhelming majority of the time - when you synced your device with your computer. There were times however, when the transfer didn't work automatically and you always had the ability to do the transfer manually. You will read about that in the link that Niel provided. Now, iTunes sees those non transferred items and warns you about them before you sync so that you have the opportunity to move them to the computer first and so that they are not erased when you sync.
Anyway, if the songs that you have on the iPad were purchased from iTunes, they will transfer back into your iTunes library when you follow the instructions in the link. If they were no purchased from iTunes, you cannot transfer them back to the Mac without using a third party app like this one.
http://www.wideanglesoftware.com/touchcopy/