iTunes cannot sync photos... Photos Library is not yet available.

We have two phones that sync from the same iTunes library. My husbands phone keeps getting the following message:

iTunes cannot sync photos to the iPhone “***'s iPhone” because your Photos Library is not yet available. Please try again later.

We both just got new iPhone 6s Plus and my husbands phone is still getting this message. My phone works fine.

Any ideas what to check? it is really frustrating not being able to figure it out.