Photos was unable to open the library “Photos Library.photoslibrary”. (3142)

Hi surfn'girl,

If you are unable to access your Photos library, check out How to use the Photos Repair Library on your Mac:

"To get to the Photos Repair Library tool on your Mac, follow these steps: 

1. If Photos is open, close the app. Then, while you click to open Photos, hold down the Command and Option keys at the same time.
2. In the window that opens, click Repair to start the repair process. You might be asked to enter your user account password.

The Repair Library tool analyzes the library's database and repairs any inconsistencies it detects. Depending on the size of your library, the repairs might take some time. When the process is done, Photos opens the library."

If still not working, use Apple Support to connect with Apple Care for further investigation.

Regards.

surfn'girl wrote:

I have had not issue, however yesterday I opened the same library from a different computer on same network.

What version of Photos did the "different" computer have? If it was newer than the version on your computer it would not be useable on your computer. You will have to update your system so that it's the same as that on the other computer. Photos libraries are not backward compatible.

However, if the system version is close to your system try opening the library with the Option+Command keys held down and see if it will repair your library. It it will then it should open with your version of Photos.