On my machine it turned out to be trying to copy a file bigger than 4gb onto a fat32 drive, so be warned, most likely to occur when copying to a nas drive, on the PC you will get no warning when copying a file bigger than 4gb onto Fat32 I beleive, you just get a corrupt file. Go for NTFS on the PC side and use the NTFS format drive accessing plugin created for MacFuse. ALthough having said that the problem was resolved by copying to a USB drive which was mac formatted rather than the internal I was trying to copying to and failing which was Fat32. So I’m assuming it was a FAT32 4gb file limit error. but hey maybe the error was the difference between copyng on the internal sata chain v external USB, but I deem that a much less likely explanation than the Fat32 4gb file limit so I would always check first to make sure your not trying to copy a file that is large than 4gb to a FAT32 fromatted drive.