Here's what worked for me: (I've had to do this a couple of times, but it seems to work).
From iTunes on my PC I selected My Phone from Devices
At the top of the page I chose Apps
I randomly moved a couple of apps around on the computer, and hit Apply (my goal was to see if it would change anything on my phone).
It went through the motions, and moved the apps on the phone.
Then, I tried to sync again.
It worked!!
I don't know why, but it did.
Before this worked, I had tried restarting the computer, changing the USB port from PC to phone, shutting down the phone and restarting, and none of that worked.
Good luck!