I am attempting to configure Photo on two macs. My MacMini has the System library and has uploaded all my picture to my iCloud photo library. I am configuring Photo on my MBP and when I enable iCloud photo library I get an error stating that the iCloud photo library can only have one system library assigned to it then the option becomes grayed out. End result...only one MAC can run Photo against the same library. Please assist.
Thank You
MacBook Pro (13-inch Mid 2012), OS X Yosemite (10.10.3)