Msg: all files will be erased and replaced with songs on this iTunes.

Question

I first set up my iPod to work on my iTunes library. Because I wanted some music from my sons iTunes, I then connected my iPod to his iTunes, created some playlists and manually moved a lot of his music into those playlists. The next time I connected iPod to my iTunes, I got the msg about all music on iPod will be erased and replaced if sync'd with my iTunes. So I chose yes and all music was deleted from iPod and all my library was sync'd back into it. However, I'm still getting the message each time I want to update on my iTunes. Could it be because I put a lot of his music into playlists which are still on my iTunes? If so, how can I remedy this?
KC

Answer 1

It has always been very basic to always maintain a backup copy of your computer for just such an occasion.
Use your backup copy of your computer to put everything on the new one.
It sounds like you have failed to do this, which is not good at all.
You will have to transfer your itunes purchases from your iphone.  Authorize your computer for your itunes account 
About iTunes Store authorization and deauthorization
Open itunes, plug in iphone, do NOT sync, click File>Transfer Purchases
When you do sync you will lose your pics ( photo library - synced from your old computer), your itunes content ( music, apps, videos,etc) , your contacts and your calendars.  So do NOT sync yet.  This is why a backup copy is so important.
Enter one unique contact and calendar entry on your computer.
When you first sync, you should get the option to merger the data.  Choose it.
If you want your pics, then you will need to e-mail them to yourself before you sync.  They will not be of the original quality as they are reduced when synced to iphone.
When all is as goos as it can be, then backup your computer, and always maintain the backup.