Plug iPhone in hoping to upload some new music to your phone but it wont connect, and instead suggests you restore factory setting (which will delete all your application data, saved games etc..)
But after researching and trying a few things this is what worked for me!
You need to download software that will enable you to browse your iPhone like a hard-drive in your Finder window on windows explorer:
-Download iExplorer3 (I used iExplorer2 for free)
– Browse your iPhone and delete this file – Media/iTunes_Control/iTunes/iTunesCDB
Deleting this database file should allow your device to sync again when you fire up iTunes. Note: This will clear the current music from your iPhone, when you upload new music the iTunesCDB file will be recreated.