iPhone 4 - iTunes wants to delete/replace my data

My wife and I both sync our iPhones to the same user account on a Macbook. Had no problems with this from the time we each got our phones. Last week, I noticed that the checkmark on Sync Apps was unchecked so I checked it. Got a message that iTunes would replace some of my apps. Tried transferring purchases from the iPhone. Did some research then crossed my fingers and synced. Ended up having to re-enter data on about 10 apps that got deleted.

Today I wanted to sync a new audiobook and noticed that ALL of the options for syncing (except those under the Info tab) were unchecked. Checking any gave me that same message about replacing the data on my iPhone. I checked the main screen when my iphone is connected and the 'manually managed my songs button is unchecked as well.

Went through and checked the ones I wanted and then hit apply only to get this message:
the iPhone "" is synced with another itunes library. do you want to erase this iphone and synce with this itunes library?

I have never synced my iPhone with any other user account or computer. I'm at a loss as to what to do and do not want to now lose all of my app data

Any suggestions??
Thanks,
E

iphone 4.0.1
Macbook with OS X 10.6.4
iTunes 9.2.1

yup...

drummingcraig said:

Do you have the "Manually Manage Music & Videos" box checked?

Click to expand...

No - I made sure that that was unchecked

Clicked on Manually manage music and got the message above - iPhone synced with another library. Want to erase and sync?

Spoke to a 'genius' today and he said there are only two options:
1. create a new user account on the mac and sync my wife's iphone to the itunes on that account

2. sync both iphones with a single itunes account. this would serve to delete any apps purchased by her and, i'm sure, would cause all kinds of havoc.

Anyone have better suggestions???
Thanks,
E