That would be an OSX or hardware problem, yes? If your external drive is formatted FAT32, and your .hdd is larger than 4 gig, the copy will fail as soon as you have 4 gig (-2 bytes) copied since that's the FAT32 file size limit. If the external isn't FAT32, you have another problem, probably either a corrupt .hdd file or a problem with the external disk. In any case, it's not a Parallels problem.