AFAIK you cant download just the viewer.
If you are sure thats its not corrupt films that are causing the problem, i recommend you backup all custom settings (Settings, Skins, Sounds, Sights, Ahiiterr and Films folder, also any screenshots you took). Then uninstall the game, then delete the game folder (it does not get removed by uninstall). Reinstall the game and copy all your custom folders back in.
