When I was copying files from a network drive to my local drive on a Mac I was receiving the error message:
The operation can’t be completed because one or more required items can’t be found.
(Error code -43)
It appears that there were some illegal characters used in the file names that cause the Finder copy to error out like that and stop the entire copy process completely.
The workaround is opening a Terminal window and entering:
cp -r sourcefolder destinationfolder/
You can simply drag and drop the source and destination folders into the terminal window to get the full path in there.
Using -r behind the cp (copy command) is necessary to ensure you go through the complete folder structure recursively.
The trailing slash at the end of the destinationfolder is necessary to ensure the folder destinationfolder gets created if it does not exist.
The copy process will now copy everything and give you a result of the files that could not be copied so you can change the filename and manually copy these over again.