Need a problem solved

I just copied some movie files off of a friends WD Passport drive onto my my WD My Book, but for some reason none of them work. I get the message “unable to play selected files …etc…”. 

These movies work on my computer and on her WD TV Live Media player, and the movies she copied off of mine work OK on her player. 

The files are a range of different types, ie: Xvid AVI. 

Anyone have any ideas.