File copying problem with mac

Hello everyone,
I got myself a new external HD to back up my pictures that are PSD, NEF and JPGs. When I try to copy pictures, some of them it gets error
"The finder cannot complete the operation because some data in DSC_1232.PSD could not be read or written. (Error code - 36)"
some files, if I copy individually it works, but some it just doesn't want to get copied.
I don't have any problems (open/save/edit) opening in photoshop. Does anyone know what might be happening???

Thanks

Peter

Two things come to mind...and we can try some others if these don't work:

1) Did you format the new drive? Some drives come FAT32 format, and if the files you are copying is large, FAT32 can't write it and it will spit out this error (can't remember if it was 2GB or 4GB limit).

2) Is there any bad connections? If you build the drive yourself, did you make sure that everything is plugged in tight? Sometimes the drive connector isn't completely on there, and when the drive spins up the vibration is enough to not make some pins connect and hence the error.