.mkv video wont allow to copy to hard drive

WD Legacy Products WD TV Live & Live Plus
1

any idea why the .mkv file i have created wont allow me to copy to my hard drive to use on the TV? i am using a mac snow lepard

2

Um, larger than 4gb (if the drive is FAT formatted)?  No permissions?  (That’s about all I can think of at the moment).