OSX - the item [-] cannot be copied because there is not enough free space.
OSX has been giving me this message copying 10Mb of files to an empty 512Mb flash memory card. So its unlikely to be correct, and its not very helpful.
I still don't know exactly why this happens, but one way around it is to copy the enclosing folder. So in my case copying to a card for a digital photo frame, I just copied the 'photos' folder, and they copied over no problem.
Some reports say that formatting the card on a real windows box in either FAT 16 or FAT 32 helps. If I get chance I'll try this.