That message either indicates that you are either trying to sync a lot more media that you think or files on your iPodare corrupt:
- for the former check your sync settings
- For the latter
Connect the iPod to your computer and look at the storage used by the various categories as shown in the colored bargarph in iTunes.
Come back with the results.
An "other" larger than about 1 1/2 GB indicates corrupted files.
What is the Other on my iPhone and How to Remove It
https://www.imobie.com/support/what-is-the-other-on-my-iphone.htm
What is "Other" and What Can I Do About It?
Reclaim "Other" storage space on iPad, iPhone and iPod
http://www.appducate.com/2013/01/reclaim-other-storage-space-on-ipad-iphone-and- ipod/
Next, usually restoring from backup eliminated the corrupted files. However, sometimes restoring to factory settings/new iPod is required.
To restore from backup see:
How to back up your iPhone, iPad, and iPod touch - Apple Supporthttp://www.appducate.com/2013/01/reclaim-other-storage-space-on-ipad-iphone-and- ipod/
To restore to factory settings/new iPod see:
Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support