Apple Photos Library Error 1000 I'm running MacOS X Catalina 10.15.2 (19C57) and have a large Photos library on a NAS. When I attempt to open Photos, I get:

"The library could not be opened." "Photos was unable to open the library “Photos Library”. (1000)"

Quit and Open Other... are the options in the error dialog box.

The library worked OK before Catalina and Photos went through an extensive library update on first launch. It sorted the pictures, but never created the or displayed the thumbnails. Now, however, it won't open the library at all.
All you have to do is hold down the OPTION and COMMAND buttons while launching Photos. You’ll need an Administrator name and password for the computer to authorize running the repair tool.

It will allow an option to Repair Library. Try to repair it and it should work if it was working without any issue before upgrade.