Have you tried the typical things of verifying the files, making sure the INI isn't looking for some non-existent BSA, and checking to make sure it's not a mod or something?
Verify the intergrity of your game cache via steam.
To do so, right click on the game in your steam game's list, go to properties on the drop down menu, and on the box that appears, go to local files, and verify game cache.