I am not a Mac user but are you sure you have all the correct permissions set for your destination drive.
I often read post here that say to "repair permissions" and this often fixes the issue.
Or do you have any unusual text characters in your file name or file path?
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10