A couple of things might have happened. Have you made sure you're trying to copy that file into "roots" home but rather "your user names" home? If that isn't the case then have you made sure that the file you were trying to copy over was not locked? either by the user or because it was created by the root user. you can always login your computer as root and change the file permissions of your user names folder or the file you are having trouble with. make sure it has full access read/write. just be careful as you don't want to change any other folder permissions.