Unable to copy pictures from "Photos Library.photoslibrary-> Show Package Contents -> Masters " to desktop

You need to use the File => Export => Export Unmodified Original

That will get you a carbon copy of the images as imported. Accessing the library package is not supported in any circumstances.

You might be right about the cause of the paste failure, but a more important point is that you are manipulating the Photos Library using something other than Photos (Finder, presumably). This is likely to cause irreparable damage to the Library.

You would probably be better to use Photos, and Folders and Albums within it, to organise your pictures. Smart Albums are a useful tool. You could move the whole Library to your central storage, if that's important to you, using Finder when Photos is closed. There are topics on here about the best way to do this.

Stephen