Help me please with a ACR DLC problem

[Man vs Wild 313]

So I downloaded arma 2 ACR because it was 10 bucks and it looked cool!

after I bought it it wouldnt show up in the expansions it only says to give a cd key when the game asks for it in the little steam pop ups

and now recently I'm getting this !!MISSING STRING ERROR every time I try to load Dayz or arma 2 oa

a little extra info is that I'm using OA and ARMA 2 free to play DayZ.

ANy help would be hugely apppreciated thanks!

[azrael000 0]

So you have ArmA2 free right?

ACR requres Orginal Full ArmA 2 and ArmA 2 OA