need help formatting hard drive

[kuatto]

Ok,formated the slave(f drive)whish is a 60g hard drive.My prime drive(c) is only 15g,so I was going to copy all files on the prime drive onto the slave and then switch out the drives so the slave becomes the prime.
The problem now is when I copy the files and start the transfer,about 3/4 into the transfer,I get message saying unable to copy some file(big long number)check to see if file is being used by other source and close.