iPhoto to Photos Shared Library Issue

It's very simple: if you're trying to share a library across accounts it must be on an external disk, formatted Mac OS Extended (Journaled) and set to ignore ownership and permissions. (This is true of iPhoto, too btw. It's quite a fluke that you haven't been having the same problem with it.)

see iPhoto: Sharing libraries among multiple users - Apple Support

Same rules hold for Photos

LN

Was there a question there?

You're mentioning two different subjects here: photo sharing and library sharing.

Currently Apple utilizes the iCloud and it's My Photo Stream, Shared Photos Streams and iCloud Photo Library to share photos. the latter can also sync libraries between devices that are signed in to the same Apple ID. However, it requires purchasing additional iCloud space to house large libraries.

For sharing libraries the Apple document that Larry provided the link for is how it must be done. The following is from that document:

To share your iPhoto library, you need to move the iPhoto library to a volume where permissions are ignored.

but for me being able open the same library (with quick access) on the internal hard drive was an easy solution for us for many years and I wish I could simply continue doing the same.

Opening a library from an external HD is no more difficult or takes more steps than from an internal HD. One you point iPhoto to that library it becomes the default library from then on. And having the library on the external HD frees up space on your boot drive.

I just upgraded to Mac OS X El Capitan and iPhoto was updated. After the update iPhoto no longer allowed me to share my photo library between accounts on the same computer. Just like you, it worked for all previous OSes (I did not upgrade to Yosemite) with the photo library existing on the \Shared internal drive. I don't understand why Apple is now blocking this feature and making the customer purchase external harddrive to share photos between accounts. This is a major back step for Apple.

While you have been lucky up to this, there have been issues with the Library in the Users/Shared folder for many version of iPhoto and the OS not just this one. The problem at heart is that you're not sharing files but a rather complex database. The database wants to control the permissions on its elements, but the Finder does too, hence the problem. Solution, put it in a place where the Finder doesn't conflict. That cannot be the start up drive - or your Mac won't start up.

Apple aren’t forcing you to do anything you know. You don't have to use iPhoto or Photos. You can use any app you prefer. You have plenty of choice.