Some users may experience an error when syncing their iPod to iTunes coded (-69). The error reads, "Attempting to copy to the disk failed. An unknown error occurred (-69)," and can be happen on Windows or Mac systems.
1. Connect your iPod to your system. Once connected, right-click (ctrl click) on the iPod icon in the Device list in iTunes.
2. Select "Sync Songs" from the menu and watch the progress bar at the top of iTunes as your songs transfer. The song file with the issue should be the last one displayed before the error message occurs. Simply remove that song from your synced playlist and sync again.
This error can also be caused by an external drive being plugged in at the same time you attempt to sync your iPod. Try removing all external devices except your iPod and syncing again. You can also reset your iPod (by pressing the menu button and the center button until the screen goes black and the Apple logo appears) or restore your iPod (by selecting "Restore" from the iPod settings tab in iTunes).