Existing iPhone 4 appearing as "welcome to your new iphone"
My dad has had an iPhone 4 for the past 7 weeks. It was initially set up and synced to his PC (running Windows XP and iTunes 10.2.2). The iPhone is running iOS 4.2.1.
Due to work commitments, dad hasn't been able to sync his phone again until now. Upon plugging the phone into his PC, iTunes displays the generic "Welcome to your new iPhone" screen... yet the iPhone has clearly been set up before on this computer! I've also plugged it into my Macbook Pro yet I'm getting the same "Welcome to your new iPhone" screen...
Any thoughts on how to fix this problem?
iPhone 4, iOS 4.2, iTunes 10.2.2