Dawn of War Codex

Hello, I'm downloading this mod for the first time on my PC, yet every time I try to download it it says that there's an error and can't open c:\program files (x86)\steam\SteamApps\common\dawn of war ii- retribution\ Elite\Archives\Elite_attrib.sga

I could really use a hand, thanks!

First try verifying integrity of game files.
Steam - Games - Dow2:Retribution, right click - local files

Correct installation goes like this:
First install DoW2: Retribution. Boot the game up at least once.
Then install 2.6.1 --> viewtopic.php?f=6&t=3076
Then install 2.7 --> viewtopic.php?f=6&t=3076