Photo library cannot be found

When I open Photos it gives the message

Photos cannot find the System Photo Library named “Photos Library”

It gives me an option to pick another one and points to the one that exists under the folder Pictures. However, if I select it the thing immediately goes back to the above. This happens on my iMac and my MacBook Air. The library is obviously there. On the iPhone and iPad I can look at pictures without a problem. I did delete that library on an old iMac that I was giving away. I rarely look at photos on my OS machines.