Error 19 (or -19): The full text of this error is: “iTunes could not sync to the iPhone ‘[iPhone name]‘ because an unknown error occurred (-19)”. This error can occur when you attempt to update an iPhone 3G to a later version of the software and iTunes attempts to back up iPhone while it is syncing. To resolve this issue:
- Deselect “Automatically sync when this iPhone is connected” from the iTunes Summary tab.
- Eject iPhone.
- Reconnect iPhone.
- Select Update.