I did exactly what you are trying to do - use the previous versions hard drive for a backup copy. I'm fully in a PC, not a Mac, and no problems just copying over. As I recall, Macs put a couple of hidden folders on their drives and folders (Resource and Fork or something along those lines) and maybe they are not allowing you to delete them even though you are running in a virtual PC mode. Even at that, I don't know why they would prevent you from copying them over. Maybe you can copy all of the PG files from the 2010 hard drive to the Mac drive, and then back to the backup usb drive. Might be something to do with usb power issues.
Good luck.