What do you think about just exporting ALL photos and then importing back. It would make a new Photo Library, would it not?
First try to copy the library over with different methods. Otherwise you will just have your photos but lost all your work - edits, keywords, albums.
Do you have cloning software like Super Duper or Canbon Copy Cloner? Then try to clone your library instead of copying. Only, this will copy any problematic files as well.
You could try to isolate the file that is giving this error.
The error -36 could also be created by a corrupted image file or video in your Photos Library.
If the Library cannot be read, and the file system on the destination drive is correct, but you can still not copy, one of the files inside may be corrupted and cannot be read. Then try to copy the library in parts. This way, you are able to identify the culprit that is causing the I/O error and can skip it, when copying:
Create a new folder on your external drive. Call it "Photos Library Copy".
Ctrl-click (or right-click) your current Photos Library and use the command "Show Package Contents". This will open a folder, showing you the files and folders inside your Photos Library.
Copy these folders one-by-one to to the new folder on your external drive. If one of these folders is giving an error -36, check how far the copying proceeded. The files, that have been copied, are o.k. The file or folder, that should have been copied next will be the unreadable file. Probably the problem is caused by one of the files in "Masters" or a database folder. In that case look into the Masters folder and copy as much as you can, while leaving out the file that will not copy.
When you are done, rename the copy of your Photos Library to "Photos Library Copy.photoslibrary" and double click it to open it in Photos. Can Photos open this library?
