photos - 'use as system photo library' greyed out
Can anyone help please? I changed from iPhoto to Photos some time ago and it worked fine. Now I find that a lot of photos are not transferring from iPhone to Mac nor the other way round. Checked the settings and find that this is what it looks like now. 'Use as System Library' is not available. How can I change this?
MacBook Pro, OS X Yosemite (10.10.5)