Photo Library to external disk

Hi. I'm saving space on my Mac and I want to move the photo library to an external disk. When I drag the folder to the disk it constantly gets the same error: finder can't complete the operation because some files can't be read or written error:-36. I repaired the photo library (alt+command) and followed all the instructions from https://support.apple.com/en-us/HT201517 and I still get the same error. How do I fix it???