If you are having problems with the SHC2 dlc after installing it, please ensure the file structure is correct by following the instructions below. Verifying the cache via Steam will not help.
Open the Stronghold Crusader 2 assets folder.
C:\Program Files (x86)\Steam\steamapps\common\Stronghold Crusader 2\assets
Within this folder you should have the following folders and files (last updated - 25/03/15).