What does it usually mean if you get 'zero bytes' message when trying to transfer files on a MacBook Air? Are the files corrupted?

What does it usually mean if you get ‘zero bytes’ message when trying to transfer files on a MacBook Air? Are the files corrupted?

Transfer how?

How big is the source folder? Are you able to access the files there?

Files weren’t opening as usual. I couldn’t even back anything up as nothing would transfer. I just turned it off for several hours and It resolved itself. I thought it would. I backed everything up.