Error message when i try to launch Arma II

[C Amendo 0]

This is the error message when i attempt to launch arma. http://i.imgur.com/l2eJd.png

Also when i attempt to join a server on the day z mod i get the error "You can not play/edit this mission; it is dependent on downloadable content that has been deleted.cherarus" I make sure i launch the game as 'Combined Operations'. Any suggestions would be great, Thanks.