IPOD Synch help please

Pennywise

I've just tried to upgrade to IOS5 and followed advice to back it up beforehand by synching it to itunes on the pc.

It is coming up with a warning that the ipod is synched to a different itunes account and saying that to continue would wipe the ipod and replace it with the itunes data and apps, i.e. trf from itunes to ipod which of course won't backup the data and games progress etc from the ipod.

Now, I've checked and both the ipod and itunes are using the same itunes account (login being the same email address). The itunes on the PC shows recent purchases of downloads, so they must be the same account, so why does itunes on the pc give a warning that they're not and threaten to delete and over-ride the ipod data etc?

The only thing I can think of is that a few months ago, I changed the email address for the itunes account, but like I say, both the ipod and itunes are now using the same itunes login.

Is there some other setting within ipod to change other than the itunes login to get rid of this warning and threat, and to enable me to backup the ipod properly to itunes?