Can't sync photos on iPhone 6+ ... because your Photos Library is not yet available.

When trying to sync photos on my Macbook Air via iTunes with my iPhone 6+ I always get the following message "iTunes cannot sync photos to the iPhone “iPhonoMe ” because your Photos Library is not yet available. Please try again later."

I've checked everything I can and can't find any solutions. I don not have this issue with my iPad...

How do I fix this?