In our house we have two iPhones and an iPad. Each one has a separate iTunes account so we could have different versions of the games instead of sharing. We've upgraded our computer from a PC to a Mac and when trying to sync any of the iPhones or iPad, we get an error message that says that the particular item is synced to a different account. How do I sync the iPhones and iPad to the new computer without erasing all the information on the item?
If you really want to sync between multiple computers, it is technically possible. You have to place your iTunes library folder in a location that can be accessed by all of the systems on the network. Then, when you want to access that shared library, hold down the Option key (Shift key on Windows) while iTunes is opening. This will bring up a dialog box with an option to select another library. Click it, and browse to the shared network folder with the iTunes library in it. iTunes will open with this library, and you should be able to sync your device on that computer.
The downside? Unless you have a server or network attached storage device, the computer that is actually hosting the iTunes library folder has to be running more or less all the time. Also, iTunes may not maintain all of its purchase authorizations between computers. If these things don't bother you, then this is definitely an option.
The message you are getting is not an error message. It is there to make sure people cant sync a device with more than one computer.
This happens for a number of reasons, One is so that your backups are on one machine and data is centralised, another is so that you cannot copy music from other people.
Before syncing, go into iTunes and authorize all the Apple ID's you have used to make purchases.
Once this is done, you can begin to sync. Plug the iDevice in and you will see the same message. Click yes.
Your device will then start to transfer all purchases on the device to the Mac.
After that it will create a backup and then start to sync media depending on what you have selected to sync
Are you syncing the data to one user on the Mac? The biggest aid would be making sure that all devices are synced to an individual user on the computer. Since your goal is to keep everything separated anyways, that is the absolute best/simplest solution I can think of. If that is what you are doing then please let me know and maybe include some screen captures of the error messages.