Setting up both DayZ and Arma2: Op Arrowhead

[Stealershock 0]

Hello everyone, first time playing both DayZ and Arma 2, but I'm having troubles getting set up. I have bought Arma2 and the expansion from steam, and successfully installed Arma2 and DayZ commander. The problem arrises however, when trying to open and play the expansion pack, when I try to do so, I am presented with the following error message

"No entry 'bin\config.bin/CfInGameUI/MPTableshadow'"

followed by

"Error compiling pixel shader PSSpecularAlpha:0"

upon which the game closes and I am left unable to play.

Assuming I need to install the expansion successfully in order to play DayZ, I have not yet tried to connect to a server using DayZ commander. Can anyone point me in the direction of the right course of action?

[pmjkerr 76]

Install both ArmA2 and Operation Arrowhead.

Then try launching with DayZ Commander. If you're still getting errors, you may need to validate files via steam.

[Stealershock 0]

I have bought and installed both games via steam, but I can only play Arma2; when I try to play the expansion, I get those error messages. How would I validate the files?