Sync issues PLEASE HELP!!
Details; My wife, two sons, and myself all have iPhones and using same computer to sync but different accounts. I recently upgraded to the 4S and wanted to give my iPhone 4 to my oldest son who has the 3gs. I performed the back up with the 3gs then restored the 4 using his backup but every time I try to sync I keep getting the same message "The iPhone cannot be synced. A duplicate file name was specified." I also received the same message when trying to sync the 3gs. WHAT GIVES??? And before someone says google it, I've tried and the only thing I can find is dealing with iTunes 9.2 and I'm using the most up to date version "10.5.1". Can someone PLEASE HELP?
Using Windows 7.