Some users have reported that they could not successfully sync all of their files resulting in this error: “(x) item(s) could not be synced. See iTunes for more information”.
Photos may cause this problem. When you sync photos to your iPhone, iPad, or iPod; iTunes creates a small version of each photo and stores them in a folder called “iPod Photo Cache.” Sometimes, inconsistencies between the real photos and photos in the cache folder may result in this error. To fix this error, simply remove the iPod Photo Cache folder(s).
Don’t worry, this folder will be recreated automatically the next time you sync photos and removing this folder will not erase your original photos. Here is how you can locate the iPod Photo Cache folder so you can drag it to your Trash (on a Mac) or Recycle Bin (on a PC). Follow: Go > Home, then open the Pictures folder and find the iPhoto Library file. Control-click the iPhoto Library and choose Show Package Contents where you can locate the iPod Photo Cache folder and drag it to the Trash. Then restart iTunes to re-initiate your sync.