Another poster wishes to help with this so creating a new thread. Copying over wifi from Mavericks onwards to a network drive, causes this error. Maybe first time, maybe it takes 4 times to copy, intermittent. Suggestions online don't work, but they may do, then doesn't. Suggestions have been: -Turn off icon preview and preview pane -Use Terminal to switch to SMB1 or CIFS -Right click the file, not fully select it when copying -I used to copy, then select and unrelated file so as to not have the file I want to copy as being selected, that seemed to work,now its playing up. My resolution was to put the file into a folder, and copy the folder, but as Graham wants to discuss, he may have other solutions, or reasons.