Error Message:
Attempting to copy to the disk failed. An unknown error occurred
Translation:
This error message generally occurs when iTunes tries to send an unusable or damaged file to your iPod.
Solution:
According to Apple, the easiest way to fix this problem is to simply remove the bad file from the list of songs to be synced. To identify which file is causing the error, press Control and click Mac (if you are using a Mac) or right-click the iPod icon and click Update (if you use Windows). Next watch the iTunes window. The name of the unusable file will appear in the display just before the error appears. Once you identify the bad file, remove it from your sync list. To do this, choose Preferences from the iTunes menu if you're on a Mac. If you're a Windows user, click Edit and then Preferences. Next click the iPod tab, then the Music tab in the iPod window. Then check the Only Update Checked Songs checkbox. Next click Library from the Source list and uncheck the checkbox next to the problematic