Finally, I’ve found the solution that has bug my iPhone 4 for the past few days. The issues appear whenever I sync my iPhone 4 to my iTunes (Mac).
Whenever I synced my iPhone, it would prompt me the following error message, “The iPhone cannot be synced. The required file can not be found” when it syncs my photos.
The solution is simple and takes less than 5 minutes. All you have to do is delete the iPod Photo Cache from the folder where you’re syncing your photos from. For example to sync with iPhoto, you’ll have to access the iPhoto Library’s iPod Photo Cache. That means, right clicking the folder > Show Package Contents to access the folder. I suppose this solution should work with other iOS devices since the way iTunes syncs the photos are the same.
If my solution doesn’t help, check out this thread: https://discussions.apple.com/message/11394784?messageID=11394784