It's best to search and read before posting questions, as this "issue" has been reported before.
http://www.gamesas.com/topic/1382257-sorry-for-this-but-i-dont-have-horse-combat-animations/page__view__findpost__p__20954695
http://www.gamesas.com/topic/1382027-the-new-pc-16-patch-through-steam-broke-the-game/page__view__findpost__p__20951245
Its the mods. Any mod that adds in custom animations screws up the game as of 1.6 due to the horse combat animations. Only option is to remove all mods that have or use custom animations.
Presumably those mods will be updated at some point.