Here's my problem and hope someone knows how to solve this: I have a window PC running Window 7. I have a Macbook running snow leopard. I attached an externalt harddrive to the window 7 PC using a powered USB hub. When I copy a file from Mac to the External HDD, it will give me the code 51 error and the file will not be copied. however, if I attached the external harddrive directly to the USB port on the window PC (ie not thru the USB Hub). The file will be copied with no issue. Does anyone knows what happens, I try to search for answers on the net and cannot find anything. please help.